BaseTools/PatchCheck: Generate error if Contributed-under found

BaseTools/PatchCheck: Generate error if Contributed-under found

https://bugzilla.tianocore.org/show_bug.cgi?id=1655

With the change to BSD+Patent License, the TianoCore Contributor's
Agreement has been removed and as a result, a Contributed-under
tag is no longer appropriate in patches.  Remove the check for
the TianoCore Contributor's Agreement and instead, generate an
error if a patch contains a Contributed-under tag in the commit
message.

Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Bob Feng <bob.c.feng@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Cc: Yonghong Zhu <yonghong.zhu@intel.com>
Signed-off-by: Michael D Kinney <michael.d.kinney@intel.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>