* Also removes the content-type check for dash+xml/mpd.
This was added in cf1f13b817d88eb7d4b449f20cbad3215030e35f,
but is a no-op since the regex pattern was never changed accordingly.
And it looks like it was unwanted anyways per 28ad7df65ddb78c16ac008886d14ae2914aea6be
Closes#12255
Authored by: mp3butcher