That flag and functionality was added in context of T304099: Structured tasks: temporary free text for "other" rejection reason. We clarified that we do not want to enable that again in the future (it is also a trust-and-safety issue). Thus the flag and the functionality of the custom input should be removed.
Acceptance criteria:
- remove GEStructuredTaskRejectionReasonTextInputEnabled and all the functionality related to the custom text-input, including its handling on the server-side from GrowthExperiments
- GEStructuredTaskRejectionReasonTextInputEnabled is removed from operations/mediawiki-config
- it is used in the same "speed-test" files as what is investigated in T379568