Remove deprecated concepts and make associated modifications

[rjyounes]

Closes #947.

[uscholdm]

@philblackwood @rjyounes
All the unitSymbol changes will be blown away. Might be a merge conflict with PR #1064

[rjyounes]

All the unitSymbol changes will be blown away. Might be a merge conflict with PR #1064

@philblackwood Can you change unitSymbol to symbol in your PR? The reference data will also need to be updated.

[philblackwood]

I removed unitSymbol, unitSymbolHtml, and unitSymbolUnicode from gistCore.ttl

I modified the release note issue1033-units-and-magnitudes to say these three deprecated properties are being removed.

I updated the data conversion script replaceProperties to replace all instance of them with gist:symbol

I did not touch any of the other deprecated properties that are in gistCore (isCharacterizedAs, isRecognizedDirectlyBy, tagText) since they are in scope of the issue #1033.

[philblackwood]

Note that gist:symbol is already in gistCore from release 12, so I did not have to change unitSymbol to symbol.

Instead, all that was needed was to remove the deprecated items unitSymbol, unitSymbolHtml, and unitSymbolUnicode.