rhbz#1001768: avoid deadlock in OAccessibleContextHelper::disposing()
rhbz#1001768: avoid deadlock in OAccessibleContextHelper::disposing()

De facto this class is locked by SolarMutex, which is what the
OExternalLockGuard actually locks;
do not lock m_Mutex because it may cause deadlock.

Change-Id: I88b226d73dbef9a5803347b0ac3191bec2ba4515

JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core