Remove now-unused AthRegSeq

As discussed on the atlas-sw-core mailing list: https://groups.cern.ch/group/atlas-sw-core/Lists/Archive/Flat.aspx?RootFolder=%2Fgroup%2Fatlas%2Dsw%2Dcore%2FLists%2FArchive%2FAthRegSeq%20used%20anywhere&FolderCTID=0x012002002A6E23175D832F4DAD957CEB680A4D57 AthReqSeq is not used for anything. This MR will remove it. From grepping the repo I see a lot of unit test references: let's see what the CI returns.

Control/AthenaCommon/python/AppMgr.py

@@ -24,7 +24,6 @@ __all__ = [ 'theApp', 'ServiceMgr', 'ToolSvc', 'AuditorSvc', 'theAuditorSvc',
             'athCondSeq',
             'athAlgSeq',    'topSequence',
             'athOutSeq',
-            'athRegSeq',
             ]
 
 ### helpers ------------------------------------------------------------------
@@ -263,7 +262,7 @@ class AthAppMgr( AppMgr ):
 
    def __build_master_sequence (self):
       """helper method to build the top-level AthSequencer from all bits and
-         pieces : AthMasterSeq, AthAlgSeq, AthOutSeq, AthRegSeq
+         pieces : AthMasterSeq, AthAlgSeq, AthOutSeq
       """
       from . import AlgSequence as _as
       from AthenaServices.AthenaServicesConf import AthIncFirerAlg as IFA
@@ -277,7 +276,6 @@ class AthAppMgr( AppMgr ):
          athAlgSeq    = _as.AthSequencer ("AthAlgSeq",IgnoreFilterPassed=True, StopOverride=True)
          athEndSeq    = _as.AthSequencer ("AthEndSeq",Sequential=True)
          athOutSeq    = _as.AthSequencer ("AthOutSeq", StopOverride=True)
-         athRegSeq    = _as.AthSequencer ("AthRegSeq", StopOverride=True)
          athAllAlgSeq = _as.AthSequencer ("AthAllAlgSeq", StopOverride=True)
          athAlgEvtSeq = _as.AthSequencer ("AthAlgEvtSeq",Sequential = True, StopOverride=True)
          # transfer old TopAlg to new AthAlgSeq
@@ -337,7 +335,6 @@ class AthAppMgr( AppMgr ):
 
          athMasterSeq += athAlgEvtSeq
          athMasterSeq += athOutSeq
-         athMasterSeq += athRegSeq
          
          Logging.log.debug ("building master sequence... [done]")
          return athMasterSeq
@@ -998,12 +995,9 @@ def AuditorSvc():             # backwards compatibility
 #                 +--- athEndSeq
 #         |
 #         +--- athOutSeq
-#         |
-#         +--- athRegSeq
 athMasterSeq = AlgSequence.AthSequencer( "AthMasterSeq" )
 athCondSeq   = AlgSequence.AthSequencer( "AthCondSeq" )
 athAlgSeq    = AlgSequence.AthSequencer( "AthAlgSeq" )
 athOutSeq    = AlgSequence.AthSequencer( "AthOutSeq" )
-athRegSeq    = AlgSequence.AthSequencer( "AthRegSeq" )
 
 topSequence  = AlgSequence.AlgSequence( "TopAlg" )     # for backward compatibility