Revert forcing use of single-parameter static_assert()

Some clang versions define static_assert as a macro apparently, so we cannot
redefine it...

This reverts commit 94bfea0ce6a7b4d5641c198d50751748a353df11.
This reverts commit 4e62627831e7457ed60ff87712570065b14b200a.

src/hb-debug.hh

diff --git a/src/hb-debug.hh b/src/hb-debug.hh
index b12c412..12b6c49 100644
--- a/src/hb-debug.hh
+++ b/src/hb-debug.hh
@@ -52,7 +52,7 @@
   int i;
   hb_options_t opts;
 };
-static_assert ((sizeof (hb_atomic_int_t) >= sizeof (hb_options_union_t)));
+static_assert ((sizeof (hb_atomic_int_t) >= sizeof (hb_options_union_t)), "");
 
 HB_INTERNAL void
 _hb_options_init (void);