Don't display usecases in IDE/REPL

It's not really useful and can be confusing.

Author: smarter

compiler/src/dotty/tools/dotc/util/ParsedComment.scala

@@ -117,7 +117,6 @@ object ParsedComment {
     "@throws"  -> TagFormatter("Throws", toDescriptionList),
     "@see"     -> TagFormatter("See Also", toMarkdownList),
     "@example" -> TagFormatter("Examples", toCodeFences("scala")),
-    "@usecase" -> TagFormatter("Usecases", toCodeFences("scala")),
     "@note"    -> TagFormatter("Note", toMarkdownList),
     "@author"  -> TagFormatter("Authors", toMarkdownList),
     "@since"   -> TagFormatter("Since", toMarkdownList),

language-server/test/dotty/tools/languageserver/HoverTest.scala

@@ -153,11 +153,6 @@ class HoverTest {
                        |   myFoo.bar[Int, String](0, "hello, world")
                        |   ```
                        |
-                       |**Usecases**
-                       | - ```scala
-                       |   def bar(fizz: Int, buzz: String): Any
-                       |   ```
-                       |
                        |**Note**
                        | - A note
                        |