Cleanup of SiSpacePointsSeedMaker_ATLxk class (ATLASRECTS-3037)

Cleanup of SiSpacePointsSeedMaker_ATLxk class

• Change the order of includes.
• Move initializations to the header file.
• Use ReadHandleKey's.
• Initialize ReadHandleKey's.
• Use Gaudi Properties.
• Add a space after if and for.
• Change if-else style for easier understanding.
• Single lines are split into multi-lines for easier understanding.
• Unify indentation.
• Use range-based for loop.
• Use static_cast.
• Remove unused variables.

RunTier0Tests.py was fine. RunTier0Tests.log