ICE/PJNATH: timer entries left in timer head after destruction

PJNATH timer heap still contains timer entries when ICE session is destroyed. The issue is reported by the following trace:

[1632775321.227|62230|ice_transport.cpp :496  ] handle events didn't finish after 6 tentatives. This is a bug. Please report it.

added to epic &22

assigned to @mchibani1

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added SprintIn progress label and removed SprintTo review label

added SprintTo review label and removed SprintIn progress label

mentioned in commit 6d4630bf

removed SprintTo review label

closed