Comments inside Schematron rules should be removed when building documentation

[martindholmes]

This issue:

TEIC/TEI#2534

was complicated by the fact that comments useful to Guidelines maintainers (but probably not to documentation readers) are currently rendered directly into the Schematron output on the spec page. These should be suppressed, making sure we don't at the same time suppress comments inside egXMLs. The different namespaces (eg vs sch) should make this relatively straightforward.

[sydb]

Does sort of beg the question of what we (or any other ODD-writer) would do if we wanted a comment to appear in the output Schematron. Use a <?tei-comment?> processing instruction?
Or, of course, we could decide the reverse: comments-in-Schematron get placed in the documentation output, but <?tei-comment?> PIs get suppressed. I actually kinda like that, myself. (In truth, though, we already use the name "tei" for comment-like processing instructions, so that might be the better name.)
There are currently only 2 comments-in-Schematron that would need to be changed.

[sydb]

Since absolutely no one has weighed in on how we should do this, and it is slowing down other tickets, I just implemented as originally suggested — PR #766 drops comments from <constraintSpec scheme="schematron"> weaving.