Remove deprecated class `iris.fileformats.rules.ProcedureRule`

[lbdreyer]

The class iris.fileformats.rules.ProcedureRule was deprecated in Iris 1.10

https://github.com/lbdreyer/iris/blob/015cee9877df87d64e84146975feb9eefea84591/lib/iris/fileformats/rules.py#L557

[DPeterK]

Closed by #2782.