InputSettingsObserver: Decouple key repeat settings from long press

Key repeat settings are now independent from long press settings, so
remove the code that handled the case where key repeat settings were
dependent on the long press settings as a fallback.

Bug: 310657006
Test: adb shell settings put secure key_repeat_timeout <value>
Change-Id: I16f1276cf04c7b2b4b794900cc498d3a1174feed