Remove negation for swift tmp file

[mzamot]

After testing PR #14570 in NC15 and Master, I couldn't write files bigger than 10MB with the negation on the verification. After removing the negation it worked just fine.

See issue #13554

read it wrong

[icewind1991]

Removing the negation here is incorrect, since it would then read use the logic for non-seekable streams for streams that are seekable and not for streams that aren't. The issue here is that streams which are seekable do not upload correctly, that either needs to be resolved or the entire check needs to be removed and we always need to do the fallback code

[schoenpat]

@icewind1991
Even if the fix isn't good, it works. Since 15.0.0 this bug exists and i'm tired of fixing it manually after every update by applying a patch. Why not accepting this pr so that in the next version swift storage is fixed and then there is enough time to develop a more beautifull fix?

[kesselb]

the entire check needs to be removed and we always need to do the fallback code

@schoenpat this would be an acceptable "fix". changing the condition like suggested is wrong. should be easy to change this pr like suggested @mzamot 🏓

[rullzer]

I remove the entire check in #15168.
So we can make sure it lands in 16.