Remove OVERRIDE_CLANG_REVISION from update_rust.py

This variable was used during the bring-up of the Rust toolchain. Now
when we want to roll Clang without Rust, we just change the clang
revision and don't change anything in the Rust variables. This works
because the package name now contains both toolchains versions in its
name.

[email protected]

Bug: 40212971
Change-Id: I334091e14531b6c03ae09587be7c9af9e854d0bf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5887217
Auto-Submit: danakj <[email protected]>
Reviewed-by: Arthur Eubanks <[email protected]>
Commit-Queue: danakj <[email protected]>
Commit-Queue: Arthur Eubanks <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1359625}
NOKEYCHECK=True
GitOrigin-RevId: ac8ff2294ca7cf4f8396bdb6115e5aafd71241ce

Author: danakj

update_rust.py

@@ -31,18 +31,9 @@
 
 # These fields are written by //tools/clang/scripts/upload_revision.py, and
 # should not be changed manually.
-#
-# In the case that a Rust roll fails and you want to roll Clang alone, reset
-# this back to its previous value _AND_ set `OVERRIDE_CLANG_REVISION` below
-# to the `CLANG_REVISION` that was in place before the roll.
 RUST_REVISION = '009e73825af0e59ad4fc603562e038b3dbd6593a'
 RUST_SUB_REVISION = 2
 
-# If not None, this overrides the `CLANG_REVISION` in
-# //tools/clang/scripts/update.py in order to download a Rust toolchain that
-# was built against a different LLVM than the latest Clang package.
-OVERRIDE_CLANG_REVISION = None
-
 # Trunk on 2022-10-15.
 #
 # The revision specified below should typically be the same as the
@@ -69,8 +60,7 @@
 
 def GetRustClangRevision():
     from update import CLANG_REVISION
-    c = OVERRIDE_CLANG_REVISION if OVERRIDE_CLANG_REVISION else CLANG_REVISION
-    return (f'{RUST_REVISION}-{RUST_SUB_REVISION}' f'-{c}')
+    return f'{RUST_REVISION}-{RUST_SUB_REVISION}-{CLANG_REVISION}'
 
 
 # Get the version of the toolchain package we already have.