Update ImageMagick to 6.9.1-6.
* Remove double --without-lcms.
* Speed up the test target by running it with multiple jobs.
* Finaly add back WITHOUT_X11 to the IM-nox11 port, this will select the
ghostscript-nox11 port instead of the x11 version. The code in
bsd.port.mk doesn't handle the OPTIONS UNSET/EXCLUDE of X11. 
PR: 199268