Clean up libutils Android.mk

Removed LOCAL_C_INCLUDES as the external/zlib headers are no longer
referenced by anything in libutils.

Removed unused host_commonLdlibs build variable. This was referenced
by the lib64utils host target which was removed in commit 03cc1f74

Tested compiling some of the projects that make use of libcutils
using a clean out dir with the folllowing targets

aosp_arm-eng : make -j16 logd dexdump
aosp-flouder-userdebug : make -j16 keystore vold libjavacore logd
aosp-x86_64-eng : make -j16 keystore vold libjavacore logd dexdump

Change-Id: I663e52bbf28dde27866dad9429bf95ada6b594a5