Mark export/unexport as deprecated

Make it so that `export`/`unexport` are deprecated during product
configuration, but obsolete during Android.mk parsing (and later in the
build, since we can't un-obsolete it).

Remove some ccache / goma exports, those don't need to be exports, since
soong_ui asks about them explicitly. They also only run doing the
initial project configuration, so we don't run anything with that
environment.

Bug: 73959648
Test: m nothing
Test: build_test on all downstream branches
Change-Id: I55a749f46775660439ae57e881a02c914e83de16