tests: Remove unneeded assert.h includes.

[Marvin]

Hi,

While running your changed tests on Windows, I think I found new failures.
Being a bot and all I'm not very good at pattern recognition, so I might be
wrong, but could you please double-check?
Full results can be found at
http://testbot.winehq.org/JobDetails.pl?Key=14540

Your paranoid android.


=== WNT4WSSP6 (32 bit mediadet) ===
mediadet.c:105: Test failed: CoCreateInstance failed with 80040154
mediadet.c:106: Test failed: pM is NULL
mediadet: unhandled exception c0000005 at 00401541

=== W2KPROSP4 (32 bit mediadet) ===
mediadet.c:105: Test failed: CoCreateInstance failed with 80040154
mediadet.c:106: Test failed: pM is NULL
mediadet: unhandled exception c0000005 at 00401541

=== W2K8SE (32 bit mediadet) ===
mediadet.c:105: Test failed: CoCreateInstance failed with 80040154
mediadet.c:106: Test failed: pM is NULL
mediadet: unhandled exception c0000005 at 00401541