Stop preprocessing String.hashCode

The internal version is only an over approximation of the behaviour.
It's better to use the version from the models.

Author: romainbrenguier

jbmc/src/java_bytecode/java_string_library_preprocess.cpp

@@ -1517,9 +1517,6 @@ void java_string_library_preprocesst::initialize_conversion_table()
   cprover_equivalent_to_java_string_returning_function[format_signature] =
       ID_cprover_string_format_func;
 
-  cprover_equivalent_to_java_function
-    ["java::java.lang.String.hashCode:()I"]=
-      ID_cprover_string_hash_code_func;
   cprover_equivalent_to_java_function
     ["java::java.lang.String.indexOf:(I)I"]=
       ID_cprover_string_index_of_func;