"make check-speed" has been broken since the removal of ninja2make
last October.  It was just a backwards-compatibility alias for
"make bench-speed", which in turn is in principle a subset of
"make bench".  Advertise the latter and drop "make check-speed"
completely since no one has noticed.

Reported-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20210310164612.285362-1-pbonzini@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Willian Rampazzo <willianr@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>