This reverts commit b6d305e4f2 because
silently discarding images using a different scale factor is simply too
user-unfriendly: this can silently break the existing code, i.e. it can
still compile perfectly and not give any errors during run-time but not
show any images neither.
Also revert most of dc43d15cf7 (Add tests of storing HiDPI images in
generic wxImageList (wxOSX, wxGTK3), 2021-04-05) as these tests don't
pass any longer because the behaviour was intentionally changed.
See #22189.
cc02b3cece