patch 8.1.1213: "make clean" in top dir does not cleanup indent test output

Problem:    "make clean" in top dir does not cleanup indent test output.
Solution:   Clean the indent test output.  Do not rely on the vim executable
            for that. (closes #4307)

runtime/indent/Makefile

@@ -11,4 +11,4 @@ test:
 
 
 clean:
-	VIMRUNTIME=$(VIMRUNTIME) $(VIM) --clean --not-a-term -u testdir/cleantest.vim
+	rm -f testdir/*.fail testdir/*.out

runtime/indent/testdir/cleantest.vim

@@ -1,11 +0,0 @@
-" Only do this with the +eval feature
-if 1
-
-  " Deletes all the test output files: *.fail and *.out
-  for fname in glob('testdir/*.out', 1, 1) + glob('testdir/*.fail', 1, 1)
-    call delete(fname)
-  endfor
-
-endif
-
-quit