Delete deprecate deprecate_uiautomation_input_injection flag

This flag was not used during the deprecation of the UiAutomation test APIs in changelist
https://googleplex-android-review.googlesource.com/q/I205f26ce9d33f5f304093ef18177d818fc3422c5.

Test: m
Flag: EXEMPT deleting unused feature flag
Bug: 277261245
Change-Id: Ib6f075ba86151256dbfa9d12a67093c9af2a2ec0