Removing string_literal declaration

This function was not used.

Author: romainbrenguier

src/java_bytecode/java_string_library_preprocess.h

@@ -286,8 +286,6 @@ class java_string_library_preprocesst:public messaget
     const std::string &s,
     symbol_tablet &symbol_table);
 
-  exprt string_literal(const std::string &s, symbol_tablet &symbol_table);
-
   codet make_function_from_call(
     const irep_idt &function_name,
     const code_typet &type,