Customizable MIME type <-> file extension mapping, step 3 (attempt #2).

This is attempt #2 to submit this CL. The first attempt failed because
some usages of MimeUtils had remained in the downstream -plus-aosp
branch. These are now cleaned up by cherry-picking the corresponding
internal master changes to that branch.

Delete unused class MimeUtils.

Some MimeUtils calls used to be on the graylist and used by some apps
through reflection; such apps can instead use this public API, for now:
android.webkit.MimeTypeMap.getSingleton().getMimeTypeFromExtension(String)
android.webkit.MimeTypeMap.getSingleton().getExtensionFromMimeType(String)

Test: Treehugger
Change-Id: I8bec5aebbbcf0a0a4a8e5dc317d188830f219a1e
3 files changed