mediafire.sh: fix

[elig0n]

Fixing failure from what seems to be obsolete parsing (file is 3 years old):

parse failed (sed): "/function[[:space:]]*_/ s/^.*"\(.\+\)";.*$/\1/p" (skip 1)
Failed inside mediafire_download(), line 333, mediafire.sh
parse_attr failed (sed): "/href/ href="
Failed inside mediafire_download(), line 336, mediafire.sh

Parsing is made a lot easier now and seems to work with /file/$FILE_ID/* URLs at least for me.
I'm not sure if the other paths are still intact though. For a trial account upload I got only such URLs.
I left the other checks though they may be obsolete too by now.

[ZLima12]

Worked for me.