I think that's the meta package that is what is updated to create a new public release. Removing it probably removes your ability to do an OTA update next PR (whenever that is).
Yeah, mp-fremantle-generic-pr is the parent package for everything, and what gets updated when there's a new release from Nokia.
If you don't put it back before Nokia release their next update, the update path may be somewhat rocky for you. The App Manager does a much better job at upgrading than apt-get does.
Why are you trying to uninstall Ovi Maps anyway? It doesn't use any resources when it's not running, unless you're really trying to scrimp on rootfs usage?
Unofficial PR1.3/Meego 1.1 FAQ
Accelemymote: make your accelerometer more joy-ful