Clean up use of NFS4ERR_BADHANDLE vs NFS4ERR_STALE

A handle that COULD be a valid Ganesha handle, that happens to not
be valid currently (for example, exportid doesn't reference a currently
valid export), or a PseudoFS ID that is in range, but not currently valid
should result in NFS4ERR_STALE.

NFS4ERR_BADHANDLE should be reserved for handles that are badly formed
or otherwise could not ever be a valid Ganesha handle.

Additionally, remove CACHE_INODE_UNAPPROPRIATED_KEY and
STATE_UNAPPROPRIATED_KEY since these errors are never used (and
were translated into NFS4ERR_BADHANDLE which is probably not the right
error if we ever did have that return code.

Signed-off-by: Frank S. Filz <ffilz@us.ibm.com>