Remove flux.tmLanguage.json

[rockstar]

With support for semantic tokens in the flux lsp, we should remove syntaxes/flux.tmLanguage.json and use the semantic token support instead. This will also allow us to find the gaps in the semantic token support.

Once this is done, we can also delete the same file from the ui.

DOD:

• Syntax highlighting is provided by the lsp, rather than a static file