Treewide: Remove python2 conditional logic/imports

[Ryanf55]

Remove conditional imports and conditional logic searching for sys.version_info that only apply to python2.

Used ChatGTP with a grepped import list to find legacy python2 module logic too.

[Ryanf55]

Here's a test plan based on the changes, I'll check off things as I go. I might request help on some of the modules like ntrip that I don't know how to use.

• [ ] Run mavproxy, import a module that doesn't exist with moddebug=3, see get_exception_stacktrace works.
• [ ] Check wx/wxagg backends warning show up for MacOS
• [ ] Check grapher can be instantiated
• [ ] Check mission_item_protocol can import
• [ ] Check mp_util can import
• [ ] Check null_term works
• [ ] Test ntrip` can be initialized and getMountPointString works
• [ ] Check params can download of param_ftp
• [ ] Test windows rline.py
• [ ] Test srtm terrain can be read
• [ ] Test wavefront import
• [ ] Check wxsettings loads the dialog
• [ ] Check dataflash logs are written and parseable
• [ ] Ensure mavproxy_devop works
• [ ] Check mavproxy_ftp can import and handle_list_reply is covered
• [ ] Check mavproxy_link imports
• [ ] Check mp_tile can import and be instantiated
• [ ] Check mavproxy_misc can be imported and cmd_playtune works
• [ ] Check mavproxy_oldwp can still import
• [ ] Check OSD param_set works
• [ ] Check mavproxy_param can import
• [ ] CHeck signing passphrase_to_key works and cmd_signing_setup works
• [ ] Check mavproxy_swarm paramString works
• [ ] Check mavproxy_useralerts can import
• [ ] Check MAVExplorer can print exceptions correctly
• [ ] Check setup.py build on windows