Remove workspaces feature flag controller

MR: Remove workspaces feature flag controller (!187247 - merged)

Description

This is tech-debt cleanup, the workspaces feature flag controller was introduced here: Fix workspaces frontend auth feature flag (!152454 - merged) as a bug fix.

Related feature flag cleanup MR: [Feature flag] Cleanup `remote_development_name... (#474784 - closed)

Issue: A new rubocop rule was introduced recently Add Cop against dynamic FF keys (!186357 - merged) which specifies that feature flag calls should static and must include a literal symbol.

The WorkspacesFeatureFlagController violates this rule and we need to fix this. As stated above this controller was introduced as a bugfix but is not being used anymore in the codebase, so i believe it is safe to remove.

Based on this review comment i believe it was scheduled for cleanup

Acceptance criteria

• References for the WorkspacesFeatureFlagController are removed
• Does not affect current functionality of workspaces
• scripts/remote_development/run-smoke-test-suite.sh passes without any errors