Use assert instead of writing out something very similar

src/core/transport/chttp2/hpack_encoder.c

@@ -365,10 +365,8 @@ static void hpack_enc(grpc_chttp2_hpack_compressor *c, grpc_mdelem *elem,
   GPR_ASSERT(GPR_SLICE_LENGTH(elem->key->slice) > 0);
   if (GPR_SLICE_START_PTR(elem->key->slice)[0] != ':') { /* regular header */
     st->seen_regular_header = 1;
-  } else if (st->seen_regular_header != 0) { /* reserved header */
-    gpr_log(GPR_ERROR,
-            "Reserved header (colon-prefixed) happening after regular ones.");
-    abort();
+  } else {
+    GPR_ASSERT(st->seen_regular_header == 0);
   }
 
   inc_filter(HASH_FRAGMENT_1(elem_hash), &c->filter_elems_sum, c->filter_elems);