Use apexd to set up chroot apex dir

Directly including elements of apexd into the otapreopt_chroot binary
has caused issues when apexd and installd fall out of sync. To avoid
this happening in the future move all apex setup into the apexd
binary and invoke it.

Bug: 181182967
Test: Manual OTA of blueline

Change-Id: I70ecff434e01e543045800ff9f8ff6b567530c33