profiles: Move PROD_INSTALL_MASK list into prod profile

The variable PROD_INSTALL_MASK is no longer used, we switch to the prod
portage profile instead these days.
profiles: exclude plain object files from prod images

There is no need to include things like glibc's lib64/crt1.o which are
only needed when compiling.
Merge pull request #860 from marineam/obj

Update production image exclude list