Revert "PT42709701 - Safer SIP transaction timers handling by usage of the OsTimerQueue"

This reverts commit 376a2e131d1d716df1e52a9380b45bf394227a11. We decided to drop this
small improvement as it came with an unexpected change in message types delivered by
timers, thus some messages were discarded by ua . Fixing this would require more risky
changes.