Remove old parsers

With the recent merge of the GML (#1752, #1793), WFS (#1829), and WMS GetCapabilities (#1610) formats, we can presumably remove the old parsers.

Code, tests, and examples are handled in separate commits, in case we want to keep one or more of them (for example, it might make sense to keep the tests for now, although we can also retrieve them later with `git revert` for example).