Don't compile libaapt with the build number

Only do that for the aapt binary itself. This will allow libaapt to be
converted to Soong.

Also remove a few lines that weren't doing anything: aaptCppflags was
never set, LOCAL_C_INCLUDES := $(LOCAL_PATH) is implied.

Test: m aapt
Test: aapt version
Change-Id: Ia3bcece14921417e1bfd3406630961c013bd497c