Remove more problematic env vars

I got a report of a user exporting CDPATH in their shell and causing
strange issues in the build. We should never need this value (and it
probably shouldn't be exported from the shell either -- that was their
workaround).

NDK_ROOT causes issues with Android.mk files thinking that they're
building with the ndk (like external/googletest/googletest/Android.mk).

Bug: 78933670
Test: CDPATH=. NDK_ROOT=test m; check out/soong.log
Change-Id: Icce43d7e31ed5e5e1fb7a4e37fd4dfbf421af4b1