Use File::Path::rmtree rather than File::Path::remove_tree

Just like File::Path::make_path, File::Path::remove_tree didn't show
up before File::Path 2.06 / perl v5.10.1, so we prefer the legacy
function here as well.
Reviewed-by: NAndy Polyakov <appro@openssl.org>

test/testlib/OpenSSL/Test.pm

@@ -46,7 +46,7 @@ use File::Copy;
 use File::Spec::Functions qw/file_name_is_absolute curdir canonpath splitdir
                              catdir catfile splitpath catpath devnull abs2rel
                              rel2abs/;
-use File::Path 2.00 qw/remove_tree mkpath/;
+use File::Path 2.00 qw/rmtree mkpath/;
 
 
 # The name of the test.  This is set by setup() and is used in the other
@@ -189,7 +189,7 @@ sub indir {
     __cwd($reverse);
 
     if ($opts{cleanup}) {
-	remove_tree($subdir, { safe => 0 });
+	rmtree($subdir, { safe => 0 });
     }
 }
 
@@ -674,7 +674,7 @@ sub __cwd {
     return undef unless chdir($dir);
 
     if ($opts{cleanup}) {
-	remove_tree(".", { safe => 0, keep_root => 1 });
+	rmtree(".", { safe => 0, keep_root => 1 });
     }
 
     # For each of these directory variables, figure out where they are relative