Remove error for asm statements in a nothrow function

From discussion:
http://forum.dlang.org/post/m02c7p$226e$1@digitalmars.com

And this check is already impossible to hit because of:
https://github.com/D-Programming-aLanguage/dmd/blob/master/src/func.c#L1778

There's already a test for this in: ``test/compilable/test11471.d`` - kinda, but druntime already depends on asm statements not causing this error in nothrow functions.

https://github.com/D-Programming-Language/druntime/blob/dbf3ff2a98208b21ee2d820df2c526af75ace863/src/core/thread.d#L2230