Revert #2705

[yuki-takeichi]

We should not use legacy filename format when uploading files by parse-server.

The change in filename format by #2705 causes a bug.
Because the filename prefixed by require('node-uuid').v4() passes the test here:
https://github.com/ParsePlatform/parse-server/pull/2001/files#diff-a5627093ba7dcdc8b5392f04905d1cafR69.
As a result all urls that point to user-owned storage are overwritten to a non-exist url that starts with http://files.parse.com/.

I know that reverting #2705 causes another problem. But it's less critical than this bug.

[yuki-takeichi]

I suggest that filename is prefixed by pssv- for example, and we should fix this code:
https://github.com/ParsePlatform/parse-dashboard/blob/57ca0e003364e16116a92bb4b6ee57a25fecf457/src/lib/getFileName.js#L15.

[flovilmart]

@yuki-takeichi that seems like a great idea, can you do that in the PR instead of the direct reverting?

[yuki-takeichi]

@flovilmart OK! I'll do that.

[flovilmart]

@yuki-takeichi any progress on that one?