In `shuffle_seq_time_offset_get()` code tried to check whether
`strips_to_shuffle` would overlap with each other, but this was done
incorrectly. This check relied on result of `shuffle_seq_test_overlap()`
but that function assumes, that only 1 strip of its input is transformed
by `offset`. This means, that if 2 strips are moved by same offset and
overlap is checked against each other it could result in true return
value. However this is checked in the code already by
`strips_to_shuffle.contains(seq_other)`, in which case loop continues.
This resulted in emmision of warning which was incorrect.
The issue is fixed by continuing loop if `strips_to_shuffle` contains
`seq_other` as first precondition to signify, that this is expected and
in fact inevitable case. `shuffle_seq_test_overlap()` does not check
whether 2 passed strips are equal, rather `BLI_assert` is used to
signify, that this is not valid use-case.
Since the warning can not happen, the logging was removed.
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