Post release 10: Remove zone-specific `server` lines from internal NTP chrony config

[jgallagher]

#6050 introduces a new boundary-ntp.control-plane.oxide.internal DNS name which resolves to "all the current boundary NTP zones" and adds it to the internal NTP chrony config, but does not remove the current zone-specific server lines like:

server 1f092e4c-eac5-408e-b421-a6b3ba8d2ce7.host.control-plane.oxide.internal iburst minpoll 0 maxpoll 4
server 6effe156-cc36-486f-82ac-2333a2fe9d87.host.control-plane.oxide.internal iburst minpoll 0 maxpoll 4

(because doing so would break NTP during the upgrade to R10). Once R10 is out the door and we know that every rack has this DNS name (which requires briefly enabling the reconfigurator system to create it), we should go back and remove these server-specific lines.