unused functions and variables

* complex.c, rational.c: remove unused functions, which are warned
  by clang 5.1, and also variables only used by removed functions.

* ext/date/date_core.c: ditto.

* enc/utf_16be.c, enc/utf_16le.c: comment out constants only used
  by commented out functions.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@45354 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
complex.c: remove f_inspect and f_to_s

* complex.c (nucomp_to_s): use rb_String.

* complex.c (nucomp_inspect): use rb_inspect.

* complex.c: use PRIsVALUE flag not to use an intermediate string
  which can be collected by GC.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@45355 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
json/parser/prereq.mk: use enum

* ext/json/parser/prereq.mk (parser.c): use `enum` instead of
  `static const int` to get rid of unused-const-variable warnings.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@45356 b2dd03c8-39d4-4d8f-98ff-823fe69b080e