[PATCH buildfix v2] tests: fix test-uncommit.t to not rely on GNU rm's flags behavior

[Augie Fackler]

# HG changeset patch
# User Augie Fackler <augie at google.com>
# Date 1505502693 14400
#      Fri Sep 15 15:11:33 2017 -0400
# Node ID 933ca2b610855d7479a2514e81b5eb9ad1c13cb4
# Parent  99a25fd51eee06baf00117114f84b630dd75f15e
tests: fix test-uncommit.t to not rely on GNU rm's flags behavior

FreeBSD rm(1) was failing thus:
> --- test-uncommit.t
> +++ test-uncommit.t.err
> @@ -299,6 +299,9 @@
>
>    $ cd ..
>    $ rm repo1 -rf
> +  rm: repo1: is a directory
> +  rm: -rf: No such file or directory
> +  [1]
>
>  Testing uncommit while merge

diff --git a/tests/test-uncommit.t b/tests/test-uncommit.t
--- a/tests/test-uncommit.t
+++ b/tests/test-uncommit.t
@@ -298,7 +298,7 @@ Uncommit leaving an empty changeset
   A Q
 
   $ cd ..
-  $ rm repo1 -rf
+  $ rm -rf repo1
 
 Testing uncommit while merge