vscode: remove the deprecated extension

Remove the deprecated SSWG Swift extension. Now that it is vended by the
Swift Language account, we don't need to explicitly recommend it as it
should be easily locatable.

Author: compnerd

.vscode/extensions.json

@@ -1,6 +1,5 @@
 {
   "recommendations": [
-    "exodiusstudios.comment-anchors",
-    "sswg.swift-lang"
+    "exodiusstudios.comment-anchors"
   ]
 }