Clean Up "code creation" feature flags

Existing groupcode creation feature flags

Ready to Be Removed

code_suggestions_completion_api

name: code_suggestions_completion_api
file: ee/config/feature_flags/development/code_suggestions_completion_api.yml
rollout_issue_url: #416371 (closed)
chatops cmd: /chatops run feature get code_suggestions_completion_api
status: Enabled globally

code_generation_no_comment_prefix

name: code_generation_no_comment_prefix
file: ee/config/feature_flags/development/code_generation_no_comment_prefix.yml
rollout_issue_url: #424879 (closed)
chatops cmd: /chatops run feature get code_generation_no_comment_prefix
status: Enabled globally

code_generation_split_by_language

name: code_generation_split_by_language
file: ee/config/feature_flags/development/code_generation_split_by_language.yml
rollout_issue_url: #427599 (closed)
chatops cmd: /chatops run feature get code_generation_split_by_language
status: Wasn't enabled

code_completion_split_by_language

name: code_completion_split_by_language
file: ee/config/feature_flags/development/code_completion_split_by_language.yml
rollout_issue_url: #427598 (closed)
chatops cmd: /chatops run feature get code_completion_split_by_language
status: Wasn't enabled

code_generation_anthropic

name: code_generation_anthropic
file: ee/config/feature_flags/development/code_generation_anthropic.yml
rollout_issue_url: #426506 (closed)
chatops cmd: /chatops run feature get code_generation_anthropic
status: Enabled globally

code_completion_anthropic

name: code_completion_anthropic
file: ee/config/feature_flags/development/code_completion_anthropic.yml
rollout_issue_url: #426111 (closed)
chatops cmd: /chatops run feature get code_completion_anthropic
status: Disabled globally

In Progress

These feature flags are still being used and should remain

skip_code_generation_instruction_extraction

name: skip_code_generation_instruction_extraction
file: config/feature_flags/development/skip_code_generation_instruction_extraction.yml
rollout_issue_url: #431246 (closed)
chatops cmd: /chatops run feature get skip_code_generation_instruction_extraction
status: Enabled for set of users