Clean up tiered storage id usage in code

There are a few places in the code where we use hard coded numbers rather than macros or known fields for tiered storage.
First, any place that looks at an object id and compares it with 0 should use WT_TIERED_OBJECTID_NONE. One known location is tiered_handle.c:245.
Second, any place that walks object ids should not use 1 to start but should use tiered->oldest_id. One known location is schema_drop.c:232.