ANDROID: sdcardfs: remove sdcardfs from system

It's no longer needed on Android devices, so remove sdcardfs core code,
and a bunch of exports that were only added so that it could be built as
a module.

Bug: 157700134
Cc: Daniel Rosenberg <drosen@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: Ic75a8cb6ed7ca7249baea4309579273e57be28ed