simplify elisp symbol accessors

simplify elisp symbol accessors

* module/language/elisp/boot.el (fset, symbol-value, symbol-function)
  (set, makunbound, fmakunbound, boundp, fboundp): Use procedures in
  `(language elisp runtime)'.
  (symbolp): New function.

* module/language/elisp/compile-tree-il.scm (set-variable!): Use
  `set-symbol-function!'.

* module/language/elisp/runtime.scm (reference-variable, set-variable!):
  Remove.
  (symbol-fluid, set-symbol-fluid!): New procedure.
  (symbol-value, set-symbol-value!, symbol-function)
  (set-symbol-function!, symbol-bound?, symbol-fbound?, makunbound!)
  (fmakunbound!): Moved from `(language elisp subrs)' and updated to
  avoid using `reference-variable' and `set-variable!'.

* module/language/elisp/runtime/subrs.scm (symbol-value)
  (symbol-function, set, fset, makunbound, fmakunbound, boundp)
  (fboundp): Move to `(language elisp runtime)'.
  (apply): Use `symbol-function'.