Fix scala#11731: Remove symbols with targetName correctly

The symbol might have original name in scope other than its current
target name (after erasure).

Author: liufengyun

compiler/src/dotty/tools/dotc/core/SymDenotations.scala

@@ -1899,7 +1899,9 @@ object SymDenotations {
      *  someone does a findMember on a subclass.
      */
     def delete(sym: Symbol)(using Context): Unit = {
-      info.decls.openForMutations.unlink(sym)
+      val scope = info.decls.openForMutations
+      scope.unlink(sym, sym.originalName)
+      scope.unlink(sym, sym.name)
       if (myMemberCache != null) myMemberCache.remove(sym.name)
       if (!sym.flagsUNSAFE.is(Private)) invalidateMemberNamesCache()
     }

tests/pos/i11731.scala

@@ -0,0 +1,5 @@
+import scala.annotation.targetName
+
+trait Example:
+  @targetName("funfun")
+  inline def fun: Unit = ???