Bug 1486690 - Remove unnecessary checks after moz_xmalloc() calls. r=glandium

There are surprisingly many of them.

(Plus a couple of unnecessary checks after `new` calls that were nearby.)

toolkit/components/url-classifier/nsUrlClassifierPrefixSet.cpp

@@ -230,7 +230,6 @@ nsUrlClassifierPrefixSet::GetPrefixes(uint32_t* aCount,
 
   uint64_t itemCount = prefixes.Length();
   uint32_t* prefixArray = static_cast<uint32_t*>(moz_xmalloc(itemCount * sizeof(uint32_t)));
-  NS_ENSURE_TRUE(prefixArray, NS_ERROR_OUT_OF_MEMORY);
 
   memcpy(prefixArray, prefixes.Elements(), sizeof(uint32_t) * itemCount);