Fix ASAN issue : heap-use-after-free

Fix ASAN issue : heap-use-after-free

- The bus message callback from gstreamer could be invoked by gmainloop
  after source element of message is released by glibc.
- This patch drops all bus messages not to be called by gmainloop in bus sync callback.
- Minor change
 : Remove unused code

[Version] 0.10.220
[Issue Type] ASAN

Change-Id: Iaa921aab14897e0f03afb6acd9a3946a2b4b63d2
Signed-off-by: Jeongmo Yang <jm80.yang@samsung.com>