Fix all unused imports flake8 warnings

lnt/lnttool/main.py:
- ignore flask.current_app and flask.g unused import warnings since they
  are used through locals() below

lnt/lnttool/__init__.py:
- ignore main.main unused import warning since it is LNT's entry point

tests/testing/cPerf.py:
- ignore lnt.testing.profile.cPerf import warning since the import is
  used to avoid a failing test if cPerf is not available

lnt/server/ui/views.py and lnt/server/ui/regression_views.py:
- remove flask.redirect imports which are no longer used since
  cc9b7c4

lnt/server/ui/globals.py:
- remove lnt.server.ui.util unused import which is no longer used since
  8082454

lnt/server/ui/decorators.py:
- remove flask.render_template unused import which is no longer used
  since f5fa093

lnt/server/db/v4db.py:
- remove sqlalchemy.orm.joinedload unused import which is no longer used
  since d464dd2

lnt/server/db/testsuitedb.py:
- remove typing.List unused import which is no longer used since
  b9d4622

lnt/server/db/migrations/upgrade_2_to_3.py,
lnt/server/db/migrations/upgrade_7_to_8.py,
lnt/server/db/migrations/upgrade_8_to_9.py and
lnt/server/db/migrations/upgrade_10_to_11.py:
- remove sqlalchemy.orm.relation unused import which was never needed

lnt/server/db/migrations/upgrade_12_to_13.py:
- remove sqlalchemy unused import which stopped being used after
  c6c4b5d (doh!)

lnt/server/db/migrations/upgrade_14_to_15.py:
- remove lnt.server.db.migrations.util.rename_table unused import which
  was never needed

lnt/server/db/rules/rule_update_profile_stats.py:
- remove datetime unused import which was never needed

tests/testing/cPerf.py:
- remove time, threading and json unused import which were never needed

tests/server/db/search.py:
- remove logging unused import which is no longer used since
  48bc5fc
- remove contextlib unused import which was never needed

tests/server/db/CreateV4TestSuite.py:
- remove sys unused import which was never needed

tests/server/db/CreateV4TestSuiteInstance.py:
- remove lnt.server.db.testsuite unused import which is no longer used
  since 7f58502

Reviewed By: cmatthews

Differential Revision: https://reviews.llvm.org/D94686

Author: Thomas Preud'homme

lnt/lnttool/__init__.py

@@ -1,2 +1,2 @@
 from __future__ import absolute_import
-from .main import main
+from .main import main  # noqa: F401  # LNT entrypoint

lnt/lnttool/main.py

@@ -65,8 +65,8 @@ def action_runserver(instance_path, hostname, port, reloader, debugger,
             app.wsgi_app, stream=open(profiler_file, 'w'),
             profile_dir=profiler_dir)
     if shell:
-        from flask import current_app
-        from flask import g
+        from flask import current_app  # noqa: F401  # Used in locals() below
+        from flask import g  # noqa: F401  # Used in locals() below
         import code
         ctx = app.test_request_context()
         ctx.push()

lnt/server/db/migrations/upgrade_10_to_11.py

@@ -3,7 +3,6 @@
 
 import sqlalchemy
 from sqlalchemy import String, Integer, Column, ForeignKey
-from sqlalchemy.orm import relation
 
 # Import the original schema from upgrade_0_to_1 since upgrade_1_to_2 does not
 # change the actual schema, but rather adds functionality vis-a-vis orders.

lnt/server/db/migrations/upgrade_12_to_13.py

@@ -1,5 +1,4 @@
 # Adds new table to store jsonschema previously used to construct testsuite.
-import sqlalchemy
 from sqlalchemy.ext.declarative import declarative_base
 from sqlalchemy import Column, String, Binary
 

lnt/server/db/migrations/upgrade_14_to_15.py

@@ -1,7 +1,7 @@
 # Drop the "FieldChange" tables; they have been deprecated and replaced by
 # "FieldChangeV2" for a long while now (but can still cause trouble when trying
 # to delete old runs that are referenced from a FieldChange entry).
-from lnt.server.db.migrations.util import introspect_table, rename_table
+from lnt.server.db.migrations.util import introspect_table
 
 
 def update_testsuite(engine, db_key_name):

lnt/server/db/migrations/upgrade_2_to_3.py

@@ -3,7 +3,6 @@
 
 import sqlalchemy
 from sqlalchemy import Integer, Column, ForeignKey
-from sqlalchemy.orm import relation
 
 # Import the original schema from upgrade_0_to_1 since upgrade_1_to_2 does not
 # change the actual schema, but rather adds functionality vis-a-vis orders.

lnt/server/db/migrations/upgrade_7_to_8.py

@@ -3,7 +3,6 @@
 
 import sqlalchemy
 from sqlalchemy import Float, String, Integer, Column, ForeignKey
-from sqlalchemy.orm import relation
 
 # Import the original schema from upgrade_0_to_1 since upgrade_1_to_2 does not
 # change the actual schema, but rather adds functionality vis-a-vis orders.

lnt/server/db/migrations/upgrade_8_to_9.py

@@ -3,7 +3,6 @@
 
 import sqlalchemy
 from sqlalchemy import String, Integer, Column, DateTime
-from sqlalchemy.orm import relation
 
 # Import the original schema from upgrade_0_to_1 since upgrade_1_to_2 does not
 # change the actual schema, but rather adds functionality vis-a-vis orders.

lnt/server/db/rules/rule_update_profile_stats.py

@@ -2,7 +2,6 @@
 Post submission hook to write the current state of the profiles directory. This
 gets fed into the profile/admin page.
 """
-import datetime
 import glob
 import json
 import os

lnt/server/db/testsuitedb.py

@@ -17,7 +17,6 @@
 from sqlalchemy import Float, String, Integer, Column, ForeignKey, Binary, DateTime
 from sqlalchemy.orm import relation
 from sqlalchemy.orm.exc import ObjectDeletedError
-from typing import List
 from lnt.util import logger
 
 from . import testsuite