Remove AdbDebuggingHandler dependency from AdbKeyStore

The dependency to request keystore persistance from AdbDebuggingHandler
is problematic. If AdbKeyStore gets eagerly initialized before
AdbDebuggingHandler and AdbKeyStore requests persistance during its
construction, then sending persist messages happens on a null instance
of AdbDebuggingHandler.

The issue isn't visible now because AdbKeyStore construction happens
lazily after AdbDebuggingHandler is fully initialized. Relying on that
lazy mechanism can be problematic if in the future we try to initialize
AdbKeyStore in a different code path where AdbDebuggingHandler isn't
fully initialized.

Test: AdbDebuggingManagerTest
Test lunch sdk_gphone64_x86_64-trunk_staging-userdebug && m && ./prebuilts/android-emulator/linux-x86_64/emulator -wipe-data -show-kernel
Bug: 420613813
Flag: EXEMPT bugfix

Change-Id: If4ce8c36eef6979a0f9e82684d93a0b1e8c95fa1