MuonConfig/MuonCombinedConfig: standardise handling of arguments

Edward Moyserequested to merge
emoyse/athena:master-fix-muonconfig into master

MuonConfig was started before we had any central handling of arguments etc in CA

This MR removes some now unneeded code, and moves to use initConfigFlags and fillFromArgs more consistently.

Tested with unit tests of affected packages.

Keeping as Draft until someone (@jojungge?) can tell me how to test the DerivationFrameworkHiggs changes (python -m DerivationFrameworkHiggs.FourLeptonVertexing --threads=1 did not work).

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