Revert "Zygote: Restrict slave mountspace so Dalvik apps can mount system-wide volumes"

No longer needed as su calls piped through the Superuser daemon run outside
zygote mountspaces.

This reverts commit a4c574321cfe9d874e69d365b1326ccc27f4e9dd.

Change-Id: I39ad8842604b5067dc3e735bcbe5fce1f3454ca8