Revert "Roll new dart_style into DEPS"

This reverts commit d6c7fe7.

Reason for revert: Error when reading 'google3:///third_party/dart/dart_style/lib/src/fast_hash.dart': File not found

Original change's description:
> Roll new dart_style into DEPS
>
> Change-Id: I4d4f71b9b244bc066e3eb00e805f21db654d699b
> Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/373724
> Commit-Queue: Konstantin Shcheglov <[email protected]>
> Reviewed-by: Samuel Rawlins <[email protected]>

Change-Id: Ieabb7b325200ef3f3b1dca386207cba9e49d2d54
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/375761
Reviewed-by: Devon Carew <[email protected]>
Commit-Queue: Konstantin Shcheglov <[email protected]>

DEPS

@@ -143,7 +143,7 @@ vars = {
   #   and land the review.
   #
   # For more details, see https://github.com/dart-lang/sdk/issues/30164.
-  "dart_style_rev": "cedd052cf1f2683019469b10966ffc6af114bac4", # disable tools/rev_sdk_deps.dart
+  "dart_style_rev": "a6ad7693555a9add6f98ad6fd94de80d35c89415", # disable tools/rev_sdk_deps.dart
   "dartdoc_rev": "f6f93ddf172716ae2a92f5e986ecbefaf9dd8a06",
   "ecosystem_rev": "2635536f8fbb13ca8349e5e461a1b45320bc01ea",
   "file_rev": "855831c242a17c2dee163828d52710d9043c7c8d",