cmssw-tool-conf: remove mpfr and gmp from skipreqtools

We need MPFR and GMP available for normal builds, otherwise CLANG and
ICC builds file. CGAL headers include headers from those two packages.

Signed-off-by: David Abdurachmanov <David.Abdurachmanov@cern.ch>
Merge pull request #1173 from davidlt/enable-mpfr-and-gmp

cmssw-tool-conf: remove mpfr and gmp from skipreqtools