Remove InsetGraphics noUnzip parameter

Remove InsetGraphics noUnzip parameter

Being able to compile document with zipped .eps files was a useful feature of
the graphicxs package 20 years ago, but the LyX support is no longer relevant:
- The flag is ignored if preview is on
- If pdflatex is used then uncompressing happens during the compilation anyway
- If set, the flag prevents LyX from issuing proper error messages if
something with the image is wrong
- For hard disk capacities from 20 years ago not uncompressing is a useful
feature, but for current hard disk capacities it does not matter
- The external inset does not have it, and if we want to merge both insets
one day we would need to implement it there, which is even more difficult
than in InsetGraphics