Fix libplatformproto includes/export includes

The host versions of these were pointing to the target generated
sources, without having proper dependencies added. But the build system
already handles these adding these to your local and exported include
directories, so just remove them.

Bug: 36365556
Test: m -j libhwui incident_report incident-section-gen
Change-Id: I52024508eabd8d10899c307c950fe045ff66ab25