libtimeinstate: open programs read-only

We only grant system_server read access to programs, but bpf_obj_get()
unnecessarily requests write as well. Instead, use bpfFdGet to open
the programs read-only

Test: programs are successfully opened & attached
Bug: 138317993
Change-Id: Icf6478737de7ea1272b995fdc7a5bd4e8947c10d
Signed-off-by: Connor O'Brien <connoro@google.com>