Rationalise use of the Pod metadata structure returned by get_pod_metadata().

Rationalise use of the Pod metadata structure returned by get_pod_metadata().

Nothing uses the entries in the 'master' array for the for the elements
flagged as 'aux', so don't generate them. Only buildtoc uses the the 'aux'
hash, and only the keys in sorted order, so replace the hash with a sorted
array.

All entries in the 'master' array are now defined, and references to 5
element arrays, so remove code that checks for this. Likewise, as the 'aux'
flag is no longer used, remove code related to it.

When generating the entries for README files in %our_pods in the consistency
checking code in get_pod_metadata, $_->[4] and $_->[1] will always be equal,
as no READMEs are copied from dual life modules. So use $_->[1] instead, as
this permits a future simplification.