i965: Switch vec4_live_variables to the non-zeroing allocator.

i965: Switch vec4_live_variables to the non-zeroing allocator.

All member variables of vec4_live_variables are already being
initialized from its constructor, it's not necessary to use rzalloc to
allocate its memory, and doing so makes it more likely that we will
start relying on the allocator to zero out all memory if the class is
ever extended with new member variables.

That's bad because it ties objects to some specific allocation scheme,
and gives unpredictable results when an object is created with a
different allocator -- Stack allocation, array allocation, or
aggregation inside a different object are some of the useful
possibilities that come to my mind.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>