New review comment by ahesford on void-packages repository

https://github.com/void-linux/void-packages/pull/22810#discussion_r459184710

Comment:
This whole `INSTALL.msg` should be gutted. The last version of radicale v1 is three years old. We should not try to hold users' hands by dumping long instructions that are unlikely to be read anyway. The entire contents of this file should be eliminated and replaced with this simple message:
```
CAUTION: Radicale 3.x is not backwards compatible with Radicale 1.x. If you are upgrading from Radicale 1.x, please consult upstream documentation for information about migrating existing data to the format used by this version.
```
Note that https://radicale.org/1to2 now returns 404, so even Radicale is not interested in helping users migrate from a long-dead version. This is not our problem to solve. If somebody is interested enough, the information can be found in the Wayback Machine.