shrink of_object_t

Reviewer: @wilmo119

Allocating and zeroing of_object_t consumes a significant amount of CPU time in my benchmarks. There were a bunch of fields that were never used, aren't used anymore, or are constant for all objects of a given class.

Before: 120 bytes
After: 32 bytes

Clients that access private fields of of_object_t will need to be updated after this goes in.