[jwplatfom] do not match video URLs(#20596)

[ipaha]

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URL 'https://content.jwplatform.com/videos/WbFsN7Kl-WdGqK18o.mp3?exp=1566156755\&sig=e60548f2434c12279baff74cf8327b9bd9ffc7383'
was broken by 7c072f0 and approach for the fix was introduced here
9c01725

[JWPlatform] WbFsN7Kl: Downloading JSON metadata
ERROR: Unable to download JSON metadata: HTTP Error 403: Forbidden (caused by HTTPError()); please report this issue on https://yt-dl.org/bug . Make sure you are using the latest version; see https://yt-dl.org/update on how to update. Be sure to call youtube-dl with the --verbose flag and include its complete output.

[dstftw]

This has no effect.

[ipaha]

I've checked the fix locally. Why you have left jwplatfom video URL broken?

[dstftw]

There are no telepathists here to know what you have checked. The URL provided does not work in both cases making this PR useless.

[ipaha]

Sorry for the mess. Just copy and past here mail text to the author of the code line I am fixing. The author is @remitamine

Here we have 2 problems after this commit 7c072f0
Broken URLS:

1. https://content.jwplatform.com/manifests/NdSc5Qlg.m3u8?exp=1554638831&sig=b7f01a3ce1e275dffe6ff74599f02ac5
2. https://content.jwplatform.com/videos/WbFsN7Kl-WdGqK18o.mp3?exp=1566156755\&sig=e60548f2434c12279baff74cf8327b9bd9ffc7383'
   Both URLs were processed in youtube_dl/extractor/common.py
   before your commit.
   And now it is processed by youtube_dl/extractor/jwplatform.py

Both errorrs the same with different ID
[JWPlatform] WbFsN7Kl: Downloading JSON metadata
ERROR: Unable to download JSON metadata: HTTP Error 403: Forbidden (caused by HTTPError());

This URL https://content.jwplatform.com/manifests/ you have fixed here 9c01725
And the output in this email chain is for manifest URL. Now manifest URL is working and processed by extractor/common.py
https://content.jwplatform.com/videos/ was fixed by me here https://github.com/ytdl-org/youtube-dl/pull/22148/files with the same approach and similar success download not listed here.

To check URL I use my paid account with temporary URL with my credentials and expiration as HTTP GET parameters ?exp=1566156755&sig=e60548f2434c12279baff74cf8327b9bd9ffc7383
That is why @dstftw can't use this url directly to check downloading.

I need to contribute the fix. Can you support?
Please

And @remitamine aswer:
the PR is not handled by me, so it would be better to explain directly on the PR.

@dstftw
Help me. Please.