sim: Remove FastAlloc

While FastAlloc provides a small performance increase (~1.5%) over regular malloc it isn't thread safe.
After removing FastAlloc and using tcmalloc I've seen a performance increase of 12% over libc malloc
when running twolf for ARM.

src/python/swig/event.i

@@ -73,7 +73,6 @@
 %include <std_string.i>
 %include <stdint.i>
 
-%import "base/fast_alloc.hh"
 %import "sim/serialize.hh"
 
 %include "base/types.hh"