Stop using canonifyURLs

[Johennes]

As reported by @zecakeh in #1937 (comment), the canonifyURLs: true setting appears to be deprecated and causes issues when used together with --baseURL. We should probably work on removing canonifyURLs.

[zecakeh]

I have managed to do that locally but we need changes to our fork of docsy, see matrix-org/docsy#3 (comment).