Remove old code relating to SystemSettings not used in new IA.

- remove activity alias: DevelopmentSettingsDashboardAlias,
DateTimeDashboardAlias, AboutDeviceDashboardAlias,
BackupResetDashboardAlias, EnterprisePrivacyDashboardAlias, and
AccessibilityDashboardAlias and updated the corresponding target
activities with the alias metadata.

- remove InputMethodAndLanguageSettingsActivity and
GestureSettingsActivity and the associated xml.

Bug: 35764802
Test: make RunSettingsRoboTests
Change-Id: I7d4922f8dfaac40e8ad077a68008185cd9fe3304