Font provider cleaning ups.

- Remove Columns.STYLE
- Decouple Context from Typeface.
- Make FontsContract constructor private since it is essentially static.
- Removed unused constants.

Bug: 37281200
Bug: 37268410
Test: am instrument -w -e class android.provider.FontsContractE2ETest
      com.android.frameworks.coretests/\
      android.support.test.runner.AndroidJUnitRunner
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.graphics.cts.TypefaceTest
      android.graphics.cts/android.support.test.runner.AndroidJUnitRunner
Change-Id: Ic46c256141d27ca28f30023bcc40f4e1161d5338