Convert BuildIgnoreApexContritbutions variable to a boolean

The ignore list is burdensome to maintain once we start adding the
module sdk contents to apex_contributions. Convert the variable to a
boolean. When set to true, all contents in `apex_contributions` will be
ignored

Bug: 308187268
Test: m nothing on aosp,google and google_fullmte devices
Ignore-AOSP-first: CL topic does a cleanup of an internal only denylist

Change-Id: Ibdd1e0d0d4f08f4f5251b9c4baa1aaf42e7df34f
Merged-In: Ibdd1e0d0d4f08f4f5251b9c4baa1aaf42e7df34f
(cherry picked from commit f3df7305d653471c70d131177e773b4723247e3a)