move srfi-1 and srfi-60 C impl to libguile, without public C api

move srfi-1 and srfi-60 C impl to libguile, without public C api

* libguile/srfi-1.c:
* libguile/srfi-1.h:
* libguile/srfi-60.c:
* libguile/srfi-60.h:
* libguile/ChangeLog-srfi: Move here, from the srfi/ dir. The C API is
  internal. Add API to register the extensions, called by init.c.

* libguile/init.c: Verily, register srfi extensions.

* libguile/Makefile.am: Add srfi files.

* module/srfi/srfi-1.scm:
* module/srfi/srfi-60.scm: Update load-extension invocation.

* Makefile.am:
* configure.ac: Remove srfi/ dir.

* test-suite/standalone/Makefile.am:
* test-suite/standalone/test-srfi-1.c: Remove srfi-1 C test, we don't
  support this API any more.