Switch back to wxWidgets 3.0 (#2131615)
When built against wxWidgets 3.2, prusa-slicer crashes on startup and is
completely unusable. Upstream recommends sticking with wxWidgets 3.0 for
now.
See https://github.com/prusa3d/PrusaSlicer/issues/8284
This reverts commit f2c45198b5f1a585c060a93ee624d580d17be791.