remove reference to SK_RELEASE, since that is automatically set based on NDEBUG (or its absence)

i.e. if NDEBUG is defined, then SK_RELEASE will get defined in the skia config headers
diff --git a/core/combo/linux-arm.mk b/core/combo/linux-arm.mk
index 6011351..6529106 100644
--- a/core/combo/linux-arm.mk
+++ b/core/combo/linux-arm.mk
@@ -112,7 +112,7 @@
 $(combo_target)GLOBAL_CPPFLAGS += -fvisibility-inlines-hidden
 
 $(combo_target)RELEASE_CFLAGS := \
-			-DSK_RELEASE -DNDEBUG \
+			-DNDEBUG \
 			-g \
 			-Wstrict-aliasing=2 \
 			-finline-functions \