Avoid system app crashes for absent TEXT_SERVICES_MANAGER_SERVICE in Wear

Wear intentionally removes the TEXT_SERVICES_MANAGER_SERVICE, so an absence of that service should not throw an exception for any app in Wear. See http://ag/q/topic:%22wear_TextServicesManagerService%22 for details.

Bug: 335456104
Bug: 366125318
Test: manual
Flag: android.server.remove_text_service
Change-Id: If17cb7fe36024f2e03cf4dd3843e99b06036cd00