Our handling of plugins when Qt is build statically is
nowadays good enough, so we don't need to build the
JPEG and GIF support directly into Qt for static builds.
Let's simply always build them as plugins.
Also simplify the logic in configure, and get rid of the
no-gif, no-jpeg and no-png config variables.
[ChangelLog][Build system] JPEG and GIF image support is now
always built as a plugin. Removed -imageformat-[jpeg|gif]
arguments to configure.
Change-Id: Ic01559ff406c966807b3be8761252e8802adcdf7
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@theqtcompany.com>