Restore ProfileGroup notification override functionality

Also clean up a little.

JIRA: CYAN-3164
Change-Id: I9b71a225996315f517b59d2d6f4074175bbf2d64
storage: Don't list removed volumes in storage list

 * Don't tell apps that USB storage or empty SD slots are available for
   use. This fixes errors about trying to create dirs in vold as well
   as the relevant CTS cases.

Change-Id: Ic763d40c19b0bb9f7497cc1515baf1661d76e9ee