Remove unused variables in system/language.

Remove unused variables in system/language.

* module/language/assembly.scm (byte-length): Don't match unused
  record slots.

* module/language/tree-il.scm (tree-il->scheme, post-order!,
  pre-order!): Likewise.

* module/language/tree-il/analyze.scm (analyze-lexicals): Likewise.

* module/language/tree-il/compile-glil.scm (flatten): Likewise.

* module/language/assembly/disassemble.scm (disassemble-load-program):
  Don't match unused list elements.

* module/language/glil/decompile-assembly.scm (decompile-toplevel,
  decompile-load-program): Likewise.

* module/system/xref.scm (program-callee-rev-vars): Likewise.

* module/language/assembly/compile-bytecode.scm
  (write-bytecode)[write-sized-loader]: Remove.

* module/language/assembly/decompile-bytecode.scm (decode-load-program):
  Factorize `pad' variables.

* module/language/ecmascript/base.scm (object->value/string,
  object->value/number)[v]: Remove.

* module/language/ecmascript/tokenize.scm (read-slash)[c0]: Remove.

* module/language/objcode/spec.scm (decompile-value)[nargs]: Remove.

* module/system/repl/command.scm (time)[vms-start, vms-end]: Remove.

* module/system/repl/repl.scm (prompting-meta-read): Use `prompt'.