Update experimental tags

[mattwthompson]

With Interchange 0.4.0, Interchange.from_openmm and Interchange.combine are no longer tagged as experimental. I'm not sure how to update the docs to examples pages to reflect that, but I'm going to try

[mattwthompson]

May be resolved by openforcefield/openff-interchange#1150 with openforcefield/openff-interchange#1149

[mattwthompson]

#72

[mattwthompson]

I could be doing something wrong (as author or consumer) but this is still being displayed and I don't think it should be

https://docs.openforcefield.org/en/latest/examples/openforcefield/openff-interchange/experimental/openmmforcefields/gaff.html