SyncFS: Drop priority field from RemoteToLocalSyncer


BUG=240165
TEST=n/a (no behavioral changes)

Review URL: https://codereview.chromium.org/96293002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@237914 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 237914