#5971 Remove deprecated context properties

[Valentin Villenave]

Skimming through define-context-properties.scm, I noticed a few deprecated props:

• bassFigureFormatFunction was dropped in 2.7.18 in favor of figuredBassFormatter.

• alignBassFigureAccidentals was deprecated even earlier, in 2.7.13.

• chordNameExceptionsFull and chordNameExceptionsPartial have been deprecated at least since I rewrote the chord naming functions in 2.21.0; the only trace left is in the chord-names-alternative snippet.

Here’s a patch to address that:
https://codereview.appspot.com/560030044/