Remove old otapreopt code in otapreopt_script.sh.

otapreopt uses the legacy dexopt code in Package Manager and is replaced
by Pre-reboot Dexopt since Android V. This change is the first step to
completely remove the legacy dexopt code from Package Manager.

Bug: 258223472
Bug: 6527146
Test: Presubmit
Flag: EXEMPT cleanup

Change-Id: Iedee5eed940e68ea2f3bd051e0cc6002e2a2c12c