TrigDecisionTool: Fix thread-safety problem.

Merged Scott Snyder requested to merge ssnyder/athena:thread.TrigDecisionTool-20221026 into master

CacheGlobalMemory::getChainGroups() is not thread-safe, since it returns a pointer to a map object which is supposed to be protected by a lock inside CacheGlobalMemory.

However, this is used only by ChainGroupFunctions::getChainGroup. Fix by removing getChainGroups() and moving the getChainGroup() logic inside CacheGlobalMemory where we can properly take the mutex.

See ATR-26495.

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