Remove dependency on MessageHandlerAutoCleanup from BasicPortAllocatorSession and AllocationSequence
Remove dependency on MessageHandlerAutoCleanup from BasicPortAllocatorSession and AllocationSequence

All Post() calls are made to the network thread which the class already
clears up explicitly. 'AutoCleanup' scans all thread instances, which is
not needed for this class.

Bug: webrtc:11988
Change-Id: Ieefbdc87683dc62b6156c5df72e87d404242170f
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/194339
Reviewed-by: Harald Alvestrand <ce816cd73d80f958d82de1df356058c2d2bca378@webrtc.org>
Commit-Queue: Tommi <74a97831ec830b6e3846c6faa50560947ae01c68@webrtc.org>
Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#32662}

TimothyGu/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc