BaseTools: remove ext_dep files for gcc

BaseTools: remove ext_dep files for gcc

Remove BaseTools/Bin/gcc_*_ext_dep.yaml to stop downloading gcc from
external locations; use the gcc provided by the container image instead.
The container image sets the variable GCC5_*_PREFIX accordingly.

Signed-off-by: Oliver Steffen <osteffen@redhat.com>
Reviewed-by: Michael Kubacki <michael.kubacki@microsoft.com>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Chris Fernald <chfernal@microsoft.com>