Remove HideFlaggedApi() related logic and the related product variables

With the recent build changes to support generating mainlin module sdk
with flagged apis, the build no longer depends on the values of these
product variables in exposing the flagged apis, but these are determined
by the aconfig flags. Given that these variables are no longer used,
this change removes these variables and the variables dependent code.

Test: m nothing --no-skip-soong-tests
Bug: 320515715
Change-Id: I6af94da73cc7fc7ffce670928aad81cec5d383b4