misc: Do not call remove_tree with `safe' set to 1.

This makes kdesrc-build fail to clean the build directories if there are
files without write permissions -- this happens if a CMake version with
automoc support is used, as AutomocInfo.cmake (aka AutogenInfo.cmake) is
written with the permissions of CMake's Auto{gen,moc}Info.cmake.in,
which can be 0444 in some systems.

REVIEW:	119263

kdesrc-build

@@ -181,7 +181,7 @@ sub prune_under_directory
 
     print "starting delete of $dir\n";
     eval {
-        remove_tree($dir, { keep_root => 1, safe => 1, error => \$errorRef });
+        remove_tree($dir, { keep_root => 1, error => \$errorRef });
     };
 
     if ($@ || @$errorRef)