user32/tests: Drop superfluous function pointer casts.

[Michael Stefaniuc]

Marvin wrote:
> 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=15553
> 
> Your paranoid android.
> 
> 
> === W7PROX64 (64 bit msg) ===
> Timeout
> 
> === TEST64_W7SP1 (64 bit msg) ===
> Timeout
No clue why the final test result line is missing but a whitespace patch
produces the exact same effect:
https://testbot.winehq.org/JobDetails.pl?Key=15555

bye
	michael