remove some deprecated things, undeprecate scm_the_root_module()

remove some deprecated things, undeprecate scm_the_root_module()

* libguile/deprecated.h
* libguile/deprecated.c (SCM_ILOC00, SCM_IDINC, SCM_IDSTMSK)
  (scm_s_expression, scm_s_test, scm_s_body, scm_s_bindings)
  (scm_s_variable, scm_s_clauses, scm_s_formals, SCM_EVALIM2)
  (SCM_EVALIM, SCM_XEVAL, SCM_XEVALCAR): Remove these macros and
  constants, deprecated in 2003.
  (scm_the_root_module): Undeprecate, it's actually a useful function,
  that other parts of the code use.

* libguile/modules.h (scm_the_root_module): Undeprecated.
* libguile/modules.c (scm_the_root_module): Rename from
  the_root_module. Use it in the rest of this file.