Remove tests that don't work on Windows.

On Windows, a filename cannot contain backslashes, because a backslash
is used directory separator. Remove tests I added in commit 9c4f5192f
that tried to do that. We could perhaps use a SKIP block to only skip
them on Windows, but I'm not sure how exactly to formulate that, so just
remove the tests to make the buildfarm green again.

Per buildfarm.

src/bin/pg_rewind/t/003_extrafiles.pl

@@ -46,16 +46,10 @@ sub run_test
 	append_to_file
 	  "$test_standby_datadir/tst_standby_dir/standby_file4 with double\"quote",
 	  "in standby4";
-	append_to_file
-	  "$test_standby_datadir/tst_standby_dir/standby_file5 with back\\slash",
-	  "in standby5";
-	append_to_file
-	  "$test_standby_datadir/tst_standby_dir/standby_file6_with_backslash\\\"and_double-quote",
-	  "in standby6";
 	mkdir "$test_standby_datadir/tst_standby_dir/standby_subdir/";
 	append_to_file
-	  "$test_standby_datadir/tst_standby_dir/standby_subdir/standby_file7",
-	  "in standby7";
+	  "$test_standby_datadir/tst_standby_dir/standby_subdir/standby_file5",
+	  "in standby5";
 
 	mkdir "$test_primary_datadir/tst_primary_dir";
 	append_to_file "$test_primary_datadir/tst_primary_dir/primary_file1",
@@ -94,10 +88,8 @@ sub run_test
 			"$test_primary_datadir/tst_standby_dir/standby_file2",
 			"$test_primary_datadir/tst_standby_dir/standby_file3 with 'quotes'",
 			"$test_primary_datadir/tst_standby_dir/standby_file4 with double\"quote",
-			"$test_primary_datadir/tst_standby_dir/standby_file5 with back\\slash",
-			"$test_primary_datadir/tst_standby_dir/standby_file6_with_backslash\\\"and_double-quote",
 			"$test_primary_datadir/tst_standby_dir/standby_subdir",
-			"$test_primary_datadir/tst_standby_dir/standby_subdir/standby_file7"
+			"$test_primary_datadir/tst_standby_dir/standby_subdir/standby_file5"
 		],
 		"file lists match");