Refactoring: simplify definition of some internal variables.

Refactoring: simplify definition of some internal variables.

In some cases, we never specbind internal objects, so they don't have
to be symbols.  Rather than using DEFSYM/DEFVAR and then uninterning
the symbols, use plain static variables.  Call staticpro for all of
them, to protect them from the garbage collector.

* src/eval.c (syms_of_eval): Use a static variable for
Qcatch_all_memory_full.

* src/emacs-module.c (syms_of_module): Use static variables for
Vmodule_refs_hash, Vmodule_runtimes, and Vmodule_environments.