tauRecTools: rename pt_combined to ptCombined

Hello,

This MR is simply renaming the combined Tau Energy Scale 4-momentum from e.g. pt_combined to ptCombined, to follow the TES naming convention. That may cause some troubles transiently, if new code is used to read old xAODs/DAODs, but it's better to do this sooner than later.

Heads up for AMG activities, @ghamity and @ademaria .

Some cleanup was also made in the tau smart slimming list.

Cheers, Bertrand