shared: Simplify buxton_hashmap_remove

Signed-off-by: Michael Ikey Doherty <michael.i.doherty@intel.com>
shared: Fix redundnant assignment in BuxtonHashmap map_resize

Signed-off-by: Michael Ikey Doherty <michael.i.doherty@intel.com>
shared: Cleanup buxton_hashmap_iter

Signed-off-by: Michael Ikey Doherty <michael.i.doherty@intel.com>