Minor javadoc improvements for PackageManager.

- Removed duplicated use of the word "the".
- Changed @return and @param explanation of getApplicationEnabledSetting,
which should get the enabled state of an application and not just one component.

Change-Id: Ide07ec84ceb5b9b5caa28efa9ba838a40ee7b514
Signed-off-by: Amaury Medeiros <amaurymedeiros@gmail.com>