UserspaceEmulator: Mark mmap regions as malloc blocks when mallocing

We don't have to be clever at all to figure out which MmapRegions are
malloc blocks, we can just mark the containing region as such when
the emulated process performs a malloc! :^)

DevTools/UserspaceEmulator/MmapRegion.cpp

@@ -65,13 +65,6 @@ MmapRegion::~MmapRegion()
         free(m_data);
 }
 
-bool MmapRegion::is_malloc_block() const
-{
-    // FIXME: This is obviously incomplete!
-    //        We should somehow know which mmap regions are malloc blocks.
-    return !m_file_backed;
-}
-
 ValueWithShadow<u8> MmapRegion::read8(FlatPtr offset)
 {
     if (!is_readable()) {