Refix Symbol leak in prepend_host_package_name

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src/hotspot/share/classfile/classFileParser.cpp

5778 Symbol* new_name = SymbolTable::new_symbol(new_anon_name,
5779 (int)host_pkg_len + 1 + class_name_len,
5780 CHECK);
5781 update_class_name(new_name);

I think calling update_class_name here is not right. new_symbol
returns a Symbol with an incremented refcount. update_class_name will
increment it again. The destructor change will decrement it, but only
once (of course). So it picked up an extra count in the process.