src: remove redundant `fflush`es on stderr
stderr has been set as no buffering.
Checklist
-
make -j4 test(UNIX), orvcbuild test(Windows) passes -
commit message follows commit guidelines
Do not update/delete: Banner broadcast message test data
Do not update/delete: Notification broadcast message test data
stderr has been set as no buffering.
make -j4 test (UNIX), or vcbuild test (Windows) passes