[Android][Mojo] Switch to standard Chromium library loader

Now that the library loader has been moved to base mojo shell can use
it. Switch to using it.

BUG=225101

Review URL: https://codereview.chromium.org/159253002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@250768 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 250768