Remove warning for tg51 addendum

[purepani]

pylinac/pylinac/calibration/tg51.py

Lines 1229 to 1233 in 3165ae3

	.. warning::
	This class uses the values of Muir & Rogers. These values are likely to be included in the new TG-51
	addendum, but are not official. The results can be up to 1% different. Physicists should use their own
	judgement when deciding which class to use. To use a manual kecal value, Pgradient and the classic TG-51 equations use
	the :class:`~pylinac.calibration.tg51.TG51ElectronLegacy` class.

This warning can (probably?) be removed since the new addendum came out last year. It should probably be confirmed that all the data is the same as in WGTG51-e though.

[mchamberland]

I have personally verified all the data, for what it's worth.

[purepani]

I was thinking of stuff more like what's actually included in the report vs the data available in the original source. I think WGTG51-e includes a more limited set of chamber calibration factors than what is included in pylinac at the moment.
Whether it actually matters to reflect this is up for debate, of course.