style: rename error functions for clarity

* src/symtab.c (symbol_redeclaration, semantic_type_redeclaration)
(user_token_number_redeclaration):
Rename as...
(complain_symbol_redeclared, complain_semantic_type_redeclared)
(complain_user_token_number_redeclared):
this.

TODO

@@ -10,7 +10,6 @@ Several features are not available in all the backends.
 ** consistency
 nonterminal vs non terminal vs non-terminal
 token vs terminal
-redeclaration vs redefinition
 
 ** yacc.c
 Now that ylwrap is fixed, we should include foo.tab.h from foo.tab.c rather