PinnerService : Avoid duplicate pins during boot up

- Remove the duplicate pin/unpins for the same apps for USER_SYSTEM
during the device boot up and unlocking phase.

- Remove the unnecessary dependency to SearchManager

Bug: 327947123
Test: atest FrameworksServicesTests:com.android.server.PinnerServiceTest
Change-Id: I78333e2bad831f67c60055eaef6cf5bcbe7ac9e9