arm-apps: Remove obmc-phosphor-license

This class is on its way to being deprecated, and oe-core packagegroups
don't have a LICENSE specified in the recipe.  Adopt the same semantics
for meta-arm.

(From meta-arm rev: beaca9ceae8bf3c75bec515cf3b2947a2051d70d)

Change-Id: I57735bbb0c9bb08907391617117e189a769ec440
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>