chore(commits): Remove dual_write_commit helper

We're no longer planning on using the dual written tables, so removing these functions

Author: wedamija

src/sentry/releases/commits.py

@@ -33,7 +33,6 @@
     PullRequestCommit,
 )
 from sentry.models.repository import Repository
-from sentry.releases.commits import _dual_write_commit
 from sentry.shared_integrations.exceptions import ApiError
 from sentry.silo.base import SiloMode
 from sentry.tasks.commit_context import PR_COMMENT_WINDOW, process_commit_context
@@ -220,7 +219,6 @@ def test_success_existing_commit(
                 author=self.commit_author,
                 key="existing-commit",
             )
-            _dual_write_commit(existing_commit)
             existing_commit.update(message="")
             assert Commit.objects.count() == 2
             event_frames = get_frame_paths(self.event)
@@ -288,7 +286,6 @@ def test_success_updating_group_owner(self, mock_get_commit_context, mock_record
                 key="existing-commit",
             )
             existing_commit.update(message="")
-            _dual_write_commit(existing_commit)
             assert Commit.objects.count() == 2
             event_frames = get_frame_paths(self.event)
             process_commit_context(
@@ -746,7 +743,6 @@ def test_time_threshold_filtering(
             key="existing-commit",
         )
         existing_commit.update(message="")
-        _dual_write_commit(existing_commit)
 
         # Map blame names to actual blame objects
         blame_mapping = {