Removal of XML parsers: pyRXP, 4suite

* Removes pyRXP from the mandatory dependencies (#1797)
* Removes 4suite (their website says to not use it anymore :haircut:)
* Some PEP8/257 :heart: 
* **NOTE** if pyRXP is installed, it will still be used instead of lxml. If anything breaks, write more tests.
586:42: E231 missing whitespace after ','
586:44: E231 missing whitespace after ','
599:17: E127 continuation line over-indented for visual indent
599:48: E228 missing whitespace around modulo operator
617:1: E303 too many blank lines (5)