[MNT]: Deprecate the axes parameter to RadialLocator

### Summary

As proposed by @anntzer in https://github.com/matplotlib/matplotlib/pull/30174#discussion_r2192130305

> Minor side point (perhaps for @QuLogic, who introduced that API): perhaps RadialLocator can again lose the second parameter to its constructor (`axes`) and just access `self.axis.axes` instead?


### Proposed fix

_No response_