Reverts "Update clang revision from 00396e6a1a0b7 to b3a9e8f7c0afb00." (flutter#48802)

Reverts flutter/engine#48705
Initiated by: zanderso
This change reverts the following previous change:
Original Description:
Previously attempted by flutter/engine#48563 but failed because of fixes needed in flutter/engine#48693

Author: auto-submit[bot]

DEPS

@@ -39,7 +39,7 @@ vars = {
   # The list of revisions for these tools comes from Fuchsia, here:
   # https://fuchsia.googlesource.com/integration/+/HEAD/toolchain
   # If there are problems with the toolchain, contact fuchsia-toolchain@.
-  'clang_version': 'git_revision:b3a9e8f7c0afb00147ab6c6a6ad426de149420dd',
+  'clang_version': 'git_revision:00396e6a1a0b79fda008cb4e86b616d7952b33c8',
 
   # The goma version and the clang version can be tightly coupled. If goma
   # stops working on a clang roll, this may need to be updated using the value