Don't print the diffs but only the actual output for checkfile-enabled tests

Author: anatoliykmetyuk

compiler/test/dotty/tools/vulpix/ParallelTesting.scala

@@ -714,16 +714,11 @@ trait ParallelTesting extends RunnerOrchestration { self =>
     def linesMatch =
       (outputLines, checkLines).zipped.forall(_ == _)
 
-    if (outputLines.length != checkLines.length || !linesMatch) {
-      // Print diff to files and summary:
-      val diff = DiffUtil.mkColoredLineDiff(checkLines :+ DiffUtil.EOF, outputLines :+ DiffUtil.EOF)
-
-      Some(
-        s"""|Output from '$sourceTitle' did not match check file.
-            |Diff (expected on the left, actual right):
-            |""".stripMargin + diff + "\n")
-    } else None
-
+    if (outputLines.length != checkLines.length || !linesMatch) Some(
+      s"""|Output from '$sourceTitle' did not match check file. Actual output:
+          |${outputLines.mkString(EOL)}
+          |""".stripMargin + "\n")
+    else None
   }
 
   /** The `CompilationTest` is the main interface to `ParallelTesting`, it