toolchain/gcc: remove dead code related to host binary stripping

The GCC_STRIP_HOST_BINARIES variable was always defined to 'nope',
which means that the host binaries were never stripped. Get rid of the
corresponding code, which is not in use.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>