scripts: remove dead file

scripts/test-driver.py was used when "make check" was already using meson
introspection data, but it did not execute "meson test".  It is dead since
commit 3d2f73e ("build: use "meson test" as the test harness", 2021-12-23).

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>