Destroy GSource object after detaching from loop

:Release Notes:
Remove memory leak of GSource

:Detailed Notes:

:Testing Performed:
Internal unit tests with valgrind
Behaviour of ls-hubd on qemux86

:QA Notes:

:Issues Addressed:
[GF-53002] ls-hubd is leaking memory

Open-webOS-DCO-1.0-Signed-off-by: Alekseyev Oleksandr<alekseyev.oleksandr@lge.com>

Change-Id: Ibd983c572ffe8351cb9c25b68c59068c987147e8
Reviewed-on: https://g2g.palm.com/4087
Reviewed-by: DCO Verification
Reviewed-by: Alekseyev Oleksandr <alekseyev.oleksandr@lge.com>
Tested-by: Alekseyev Oleksandr <alekseyev.oleksandr@lge.com>
Reviewed-by: Keith Derrick <keith.derrick@lge.com>