Revert "[scudo] Enable MemMapFuchsia"

This reverts commit 145a929.

Author: fabio-d

compiler-rt/lib/scudo/standalone/mem_map.h

@@ -76,7 +76,7 @@ class ReservedMemoryDefault final
 using ReservedMemoryT = ReservedMemoryDefault;
 using MemMapT = ReservedMemoryT::MemMapT;
 #elif SCUDO_FUCHSIA
-using ReservedMemoryT = ReservedMemoryFuchsia;
+using ReservedMemoryT = ReservedMemoryDefault;
 using MemMapT = ReservedMemoryT::MemMapT;
 #elif SCUDO_TRUSTY
 using ReservedMemoryT = ReservedMemoryDefault;