Remove unused top-level variables.

Remove unused top-level variables.

* module/ice-9/runq.scm (fork-strips): Remove.

* module/language/assembly.scm (*block-alignment*): Remove.

* module/language/assembly/disassemble.scm (disassemble-objects,
  simplify): Remove.

* module/srfi/srfi-18.scm (mutex-owners): Remove.

* module/srfi/srfi-19.scm (leap-year?): Remove.

* module/system/base/compile.scm (dsu-sort): Remove.

* module/texinfo.scm (ascii->char): Remove.

* module/texinfo/html.scm (ignored?): Remove.

* module/texinfo/indexing.scm (def-name): Remove.

* module/texinfo/plain-text.scm (ignore): Remove.