Legacy fix for AlgContextSvc (GAUDI-1305)
Remove the thread-local algorithm stack again as this breaks the timeout handling in the ATLAS HLT (ATR-16745). For GaudiMT we need anyway a completely different solution. But for the v27r1 branch that we use in 21.1 this is the simplest solution.
Also cherry-picked gaudi/Gaudi!362 (merged) so I could even compile this on my local machine.