PackageManager: remove INSTALL_PARSE_FAILED_ONLY_COREAPP_ALLOWED

Due to the removal of support for Full Disk Encryption and the related
"core apps only" mode of system_server, this error code is never
returned.  It is marked with @hide, so we can just remove it after
removing the only users of it, in ApexPackageInfo and
InstallPackageHelper.

Bug: 208476087
Change-Id: Ie53c41ef3c346e6a9210836e3d842cee966d7924