pc: completions - do not add [] for ... derives TC@@ (#23811)

Currently it incorectly adds completion members with square brackets.
Exmaple:
```scala
class X derives CanEqua@@ // returns `CanEqual[@@]` and `CanEqual`
                          // should return only `CanEqual`
```

Author: dos65

presentation-compiler/test/dotty/tools/pc/tests/completion/CompletionSuite.scala

@@ -2285,3 +2285,11 @@ class CompletionSuite extends BaseCompletionSuite:
         |""".stripMargin,
       "asTerm: Term"
     )
+  
+  @Test def `derives-no-square-brackets` =
+    check(
+      """
+        |case class Miau(y: Int) derives Ordering, CanEqu@@
+        |""".stripMargin,
+      "CanEqual scala"
+    )