Revert "hammerhead: switch back to dlmalloc"

This reverts commit 79906085f6fe832b92fe9095fd251e1db26ede55.

Didn't do anything for:

b/18069309 N5 running L can't run as many apps simultaneously as running K

Change-Id: I9c5ed4257f2162757c6e147e396af882ecef913c
diff --git a/BoardConfig.mk b/BoardConfig.mk
index 4f1142b..fd48f5e 100644
--- a/BoardConfig.mk
+++ b/BoardConfig.mk
@@ -155,7 +155,5 @@
 # Enable Minikin text layout engine (will be the default soon)
 USE_MINIKIN := true
 
-MALLOC_IMPL := dlmalloc
-
 # Include an expanded selection of fonts
 EXTENDED_FONT_FOOTPRINT := true