Phiscally remove the ignored Scala 2 library-aux files instead of fil…

…tering them out in `Compile / sources` (not reliable, for some reasone the AnyRef.scala was still compiled)

project/Build.scala

@@ -1124,19 +1124,23 @@ object Build {
           IO.createDirectory(trgDir)
           IO.unzip(scalaLibrarySourcesJar, trgDir)
 
-          ((trgDir ** "*.scala") +++ (trgDir ** "*.java")).get.toSet
+          val (ignoredSources, sources) =
+            ((trgDir ** "*.scala") +++ (trgDir ** "*.java")).get.toSet
+              .partition{file =>
+                // sources from https://github.com/scala/scala/tree/2.13.x/src/library-aux
+                val path = file.getPath.replace('\\', '/')
+                path.endsWith("scala-library-src/scala/Any.scala") ||
+                path.endsWith("scala-library-src/scala/AnyVal.scala") ||
+                path.endsWith("scala-library-src/scala/AnyRef.scala") ||
+                path.endsWith("scala-library-src/scala/Nothing.scala") ||
+                path.endsWith("scala-library-src/scala/Null.scala") ||
+                path.endsWith("scala-library-src/scala/Singleton.scala")
+              }
+          // These sources should be never compiled, filtering them out was not working correctly sometimes
+          ignoredSources.foreach(_.delete())
+          sources
         } (Set(scalaLibrarySourcesJar)).toSeq
       }.taskValue,
-      (Compile / sources) ~= (_.filterNot { file =>
-        // sources from https://github.com/scala/scala/tree/2.13.x/src/library-aux
-        val path = file.getPath.replace('\\', '/')
-        path.endsWith("scala-library-src/scala/Any.scala") ||
-        path.endsWith("scala-library-src/scala/AnyVal.scala") ||
-        path.endsWith("scala-library-src/scala/AnyRef.scala") ||
-        path.endsWith("scala-library-src/scala/Nothing.scala") ||
-        path.endsWith("scala-library-src/scala/Null.scala") ||
-        path.endsWith("scala-library-src/scala/Singleton.scala")
-      }),
       (Compile / sources) := {
         val files = (Compile / sources).value
         val overwrittenSourcesDir = (Compile / scalaSource).value