Kill BOARD_MALLOC_ALIGNMENT.

Bug: http://b/26403338
Change-Id: Iba4006277fdb7c7ca60542c517634ae86c847b4f

libc/Android.bp

@@ -112,11 +112,6 @@ cc_defaults {
         device_uses_dlmalloc: {
             cflags: ["-DUSE_DLMALLOC"],
         },
-        // To customize dlmalloc's alignment, set BOARD_MALLOC_ALIGNMENT in
-        // the appropriate BoardConfig.mk file.
-        dlmalloc_alignment: {
-            cflags: ["-DMALLOC_ALIGNMENT=%d"],
-        },
     },
     // Clang/llvm has incompatible long double (fp128) for x86_64.
     // https://llvm.org/bugs/show_bug.cgi?id=23897

libc/Android.mk

@@ -655,13 +655,6 @@ else
   libc_common_c_includes += external/jemalloc/include
 endif
 
-# To customize dlmalloc's alignment, set BOARD_MALLOC_ALIGNMENT in
-# the appropriate BoardConfig.mk file.
-#
-ifneq ($(BOARD_MALLOC_ALIGNMENT),)
-  libc_common_cflags += -DMALLOC_ALIGNMENT=$(BOARD_MALLOC_ALIGNMENT)
-endif
-
 # Define some common conlyflags
 libc_common_conlyflags := \
     -std=gnu99