tests: fp: remove unused submodules

tests/fp/berkeley-softfloat-3 and tests/fp/berkeley-testfloat-3
have been replaced by subprojects, so remove the now-unnecessary
submodules.

Reported-by: Michal Privoznik <mprivozn@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

berkeley-softfloat-3 @ b64af41c

-Subproject commit b64af41c3276f97f0e181920400ee056b9c88037

berkeley-testfloat-3 @ 40619cbb

-Subproject commit 40619cbb3bf32872df8c53cc457039229428a263