Only dexpreopt system server jars for the primary arch.

This change stops the build system from dexpreopting system server jars
for the secondary arch. System server jars are only loaded by the system
server, so the artifacts for the the secondary arch are not used.

Bug: 260577273
Test: Build a system image and no longer see artifacts for the
  secondary arch.
Change-Id: I0b131a02e996ed50e7aec3bb0a221f8ceed9ce57