Remove asserts that confuse `enum _framestate` with `enum _frameowner` (GH-124148)

The `owner` field of `_PyInterpreterFrame` is supposed to be a member of
`enum _frameowner`, but `FRAME_CLEARED` is a member of `enum _framestate`.

At present, it happens that `FRAME_CLEARED` is not numerically equal to any
member of `enum _frameowner`, but that could change in the future. The code
that incorrectly assigned `owner = FRAME_CLEARED` was deleted in commit
a53cc3f49463e50cb3e2b839b3a82e6bf7f73fee (GH-116687). Remove the incorrect
checks for `owner != FRAME_CLEARED` as well.