post 531 actions - deprecating gist:symbolUnicode and gist:symbolHtml

[pwin]

Fixes #992.

[uscholdm]

These should be removed, not deprecated. Here is why.

This is very confusing. I'm not exactly sure what is going on. @rjyounes It looks like the net effect of what we ended up doing was to rename unitSymbol to symbol and to remove unitSymbolUnicode and unitSymbolHtml, but we did it in two steps:

1. First we 'renamed' unitSymbol, and unitSymbolUnicode and unitSymbolHtml, to unitSymbol, symbol and symbolUnicode and symbolHtml,. By rename, I mean we deprecated the original and created new properties.
2. We removed symbolUnicode and symbolHtml

Normally we do not remove things except on a major release, but in this case we are not removing anything we added during this release, we are removing something we created during this release that we then removed.