Conditionally remove oahl from bootclasspath

If REMOVE_OAHL_FROM_BCP=true then this adds the
framework-oahl-backward-compatibility library to the bootclasspath.

Otherwise, it adds the org.apache.http.legacy instead.

Bug: 18027885
Bug: 72375096
Test: build, flash and test manually and with FrameworkCoreTests
Change-Id: I17170f873eec93b2e2ed7be3459e2d28c96bbe4c