Revert "Accept decay rate parameter in MockCompilationRunner"

This reverts commit 37a6c90.

These apparently were there for a reason. The tests all passed on my
system which is interesting. Not sure if it's an environment difference
or what, but will investigate more thoroughly later.

Author: boomanaiden154

compiler_opt/tools/generate_default_trace_test.py

@@ -33,8 +33,7 @@
 class MockCompilationRunner(compilation_runner.CompilationRunner):
   """A compilation runner just for test."""
 
-  def __init__(self, moving_average_decay_rate: float, sentinel=None):
-    del moving_average_decay_rate  # Unused.
+  def __init__(self, sentinel=None):
     assert sentinel == 42
     super().__init__()