log: remove spice_static_assert macro

The macro was misused and not doing static check.
Spice have other working static check macros to use.
The macro is used only by spice-common so removing it
does not cause issues to other depending projects.

Signed-off-by: Frediano Ziglio <fziglio@redhat.com>
Acked-by: Marc-André Lureau <marcandre.lureau@redhat.com>