remove mmacros, SCM_SYNTAX snarf macro

remove mmacros, SCM_SYNTAX snarf macro

* libguile/snarf.h (SCM_SYNTAX): Remove snarf macro, users can't define
  primitive syntax any more.

* libguile/memoize.c (SCM_SYNTAX): Define locally, and just call
  scm_i_makbimacro as there's no difference between that and
  scm_makmmacro. Alter invocations to suit.

* libguile/macros.h:
* libguile/macros.c (scm_i_makmmacro): Remove; users can't define
  primitive syntax any more. Use define-syntax instead.
  (scm_make_synt): Remove, this was only used by the SCM_SYNTAX snarf
  macro.
  (scm_i_makbimacro): Change prototype of this internal function to make
  the gsubr on behalf of the caller.
  (macro_print, scm_macro_type): Remove cases for mmacros.