Remove individual functions deprecated before 0.41

More towards #8751.

The following APIs are removed with this PR, listed along side the commit they were deprecated with and the release that deprecation went into effect.

* `FileUtils.canonicalizeFolderPath()` (a9ab07c38e2175c46bccaa3c5ad8fb3e331b7499, 0.33)
* `LiveDevelopment/Agents/CSSAgents.getStylesheetURLs()` (04b015e9d18a44b1f27c889c12d36b8abacc06cc, 0.37)
* `LiveDevelopment/Documents/CSSDocument.getStyleSheetFromBrowser()` (d2a8a827454efe4e692fa17730e36649cb19a1dd, 0.37)
* `ProjectManager.isBinaryFile()` (0c0218454c5dfea62ced4f3ec75de34bee13930c, 0.39)

There is only instance any of these APIs are used, and that is `getStylesheetURLs()` in the `relution.brackets` extension by http://www.relution.io/en/, and that is because they have duplicated that module in their extension (possibly with changes just for them).
That's what I thought too, but Travis failed when I removed it because it is referenced in the block at lines 307-320.