Remove execmem permission from domain, add to appdomain.

execmem permission controls the ability to make an anonymous
mapping executable or to make a private file mapping writable
and executable.  Remove this permission from domain (i.e.
all domains) by default, and add it explicitly to app domains.
It is already allowed in other specific .te files as required.
There may be additional cases in device-specific policy where
it is required for proprietary binaries.

Change-Id: I902ac6f8cf2e93d46b3a976bc4dabefa3905fce6
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>