Revert "Don't use framework strings for formatting file sizes"

This reverts commit ded99003.

- Add java import in order to build successfully
- Fix RunSettingsRoboTests

Test: adb shell am instrument -w -e class
com.android.settings.utils.FileSizeFormatterTest
com.android.settings.tests.unit/android.support.test.runner.AndroidJUnitRunner
Test: make -j RunSettingsRoboTests
Bug: 70005649
Bug: 36994779
Change-Id: I1c0ff48c749e9fbb82fd670c27243bd3922ed373