Which library features appear in the main index is inconsistent

[jwakely]

Most library components are not in the main index (just the headers), but the random numbers subclause adds several entries:

Also every enumerator of the regex_constants::syntax_option_type is index, e.g. awk and multiline.

We should either consistently index all library enumerators and classes in the main index, or remove many of the entries that come from <random> and <regex>.

The following may be useful, but probably not all the others:

[jensmaurer]

Editorial meeting: Avoid listing library names in the main index. We should not have \tcode entries from the library in the main index. Also excise headers from the main index.