Font API clean up

- Move FontRequest from android.graphics.fonts to android.provider since
  this is only used by android.provider.FontsContract and never draw
  anything.
- FontRequest is no longer being Parcelable.
- Remove FontSpec.aidl which is not necessary.

Bug: 37326126
Test: am instrument -w -e class android.provider.FontsContractTest
      com.android.frameworks.coretests/\
      android.support.test.runner.AndroidJUnitRunner
Test: am instrument -w -e class android.provider.cts.FontProviderTest
      android.provider.cts/android.support.test.runner.AndroidJUnitRunner
Test: am instrument -w -e class android.provider.cts.FontRequestTest
      android.provider.cts/android.support.test.runner.AndroidJUnitRunner

Change-Id: I0eb501844247c2f07eaa1fc7a71f72e404888b5b