um: Remove dead usage of TIF_IA32

This seems like a dead artifact since TIF_IA32 is not even defined as a
TI flag for UM.  Looking back in git history, it made sense in the old
days, but it is apparently not used since UM was split out of the x86
arch/.  It is also going away from the x86 tree soon.

Also, I think the variable clean up it performs is not needed as 64-bit
UML doesn't run 32-bit binaries as far as I can tell, and 32-bit UML
has 32-bit ulong.

Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com>
Signed-off-by: Richard Weinberger <richard@nod.at>