Remove deprecated PP legacy_custom_rules

[DPeterK]

The legacy_custom_rules in iris.fileformats.rules were deprecated in v1.9 and made life unnecessarily difficult in #2059. As the functionality has served its deprecation period, let's just remove it for v1.10.

[DPeterK]

@bjlittle FYI it's just pesky timeout exceptions that are now stopping the tests from passing 😒

[marqh]

Hi @dkillick

what is the purpose of the file:
.idea/uiDesigner.xml
please?

[DPeterK]

@marqh that's a file for an IDE, which should not have been included in the commit. Frankly, I'm surprised it was; I'll get rid of it.

[marqh]

The legacy_custom_rules in iris.fileformats.rules were deprecated in v1.9 and made life unnecessarily difficult in #2059. As the functionality has served its deprecation period, let's just remove it for v1.10.

I think this may be a bit hasty. There is user feedback regarding use of this feature which we are managing.
It may be less disruptive to remove this at a later version than 1.10.
I'm not sure about this, but I think we should consider it

[pelson]

@dkillick - I think we need to understand where this one is at. Do we need it for 2.0? Can we close this PR altogether? etc.
Would you mind providing a status update?

[DPeterK]

The legacy_custom_rules were actually removed in #2778... think this is done.