apexd: Remove monitorBuiltinDirs

With apexd becoming a lazy aidl, this code is now never actually
executed. We should find a different way of hot-swapping active apexes
via `adb sync`...

Test: builds
Test: device boots
Bug: 155275196
Change-Id: I7e4c1ad5bf4b2a2d9639c3544bd1ad66a2934e96
4 files changed