Remove ID of unimplemented string function

The string function with ID_cprover_string_concat_long_func was unimplemented
and will be obsolete when the functionality is handled by a model.

Author: danpoe

jbmc/src/java_bytecode/java_string_library_preprocess.cpp

@@ -1752,9 +1752,6 @@ void java_string_library_preprocesst::initialize_conversion_table()
   cprover_equivalent_to_java_assign_and_return_function
     ["java::java.lang.StringBuffer.append:(C)Ljava/lang/StringBuffer;"]=
       ID_cprover_string_concat_char_func;
-  cprover_equivalent_to_java_assign_and_return_function
-    ["java::java.lang.StringBuffer.append:(J)Ljava/lang/StringBuffer;"]=
-      ID_cprover_string_concat_long_func;
   cprover_equivalent_to_java_assign_and_return_function
     ["java::java.lang.StringBuffer.append:(Ljava/lang/String;)"
       "Ljava/lang/StringBuffer;"]=

src/util/irep_ids.def

@@ -596,7 +596,6 @@ IREP_ID_ONE(cprover_string_code_point_count_func)
 IREP_ID_ONE(cprover_string_offset_by_code_point_func)
 IREP_ID_ONE(cprover_string_compare_to_func)
 IREP_ID_ONE(cprover_string_concat_func)
-IREP_ID_ONE(cprover_string_concat_long_func)
 IREP_ID_ONE(cprover_string_concat_char_func)
 IREP_ID_ONE(cprover_string_concat_code_point_func)
 IREP_ID_ONE(cprover_string_constrain_characters_func)