Fix scripted test i7897

- Move build-no-fork.sbt in a subdirectory, otherwise it would be loaded
  by sbt.
- Call reload after changing build.sbt, otherwise nothing ould actually
  change.
- Remove build.properties, no longer needed since we now use sbt 1.3.6
  by default.

Author: smarter

sbt-dotty/sbt-test/sbt-dotty/i7897/build-no-fork.sbt

@@ -1,3 +1,4 @@
 > run
-$ copy-file build-no-fork.sbt build.sbt
+$ copy-file changes/build-no-fork.sbt build.sbt
+> reload
 > run