removed useless code

In destructors, zeroing attributes or clearing containers is utterly useless.

code/Common/DefaultIOStream.cpp

@@ -82,7 +82,6 @@ inline int select_fseek<8>(FILE *file, int64_t offset, int origin) {
 DefaultIOStream::~DefaultIOStream() {
     if (mFile) {
         ::fclose(mFile);
-        mFile = nullptr;
     }
 }