libcupsfilters: In ghostscript() do not use gray profile on color PCLm

libcupsfilters: In ghostscript() do not use gray profile on color PCLm

The "pclm" output device of Ghostscript only supports 8-bit sRGB
output, no sGray and also no color-to -monochrome conversion. There is
also no way to convert to grayscale by simply applying a gray color
profile.

Applying the gray color profile caused a crash in older versions of
Ghostscript and now is rejected with an error. See

    https://bugs.ghostscript.com/show_bug.cgi?id=705014