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.

[peterbarker]

Has to pass CI.

How was this tested?

[Ryanf55]

Finish before merge

[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