Always use our copy of libz

Instead of hoping that the host libz is compatible with our build time
stubs.

Test: m etc1tool
Change-Id: I4fe25cd0d265895baf8db1f182f96b171e0c84b6

Author: danw

tools/etc1tool/Android.mk

@@ -12,13 +12,8 @@ LOCAL_SRC_FILES := etc1tool.cpp
 LOCAL_STATIC_LIBRARIES := \
 	libexpat \
 	libpng \
-	libETC1
-
-# Statically link libz for MinGW (Win SDK under Linux),
-# and dynamically link for all others.
-LOCAL_STATIC_LIBRARIES_windows := libz
-LOCAL_LDLIBS_darwin := -lz
-LOCAL_LDLIBS_linux := -lrt -lz
+	libETC1 \
+	libz
 
 LOCAL_MODULE := etc1tool
 LOCAL_MODULE_HOST_OS := darwin linux windows