Remove `maxlength` limit from the project description textarea

In the `General Settings` page one can add an optional project
description. Previously, this textarea field was set to a maximum of
250 characters. In this commit we have remove that limit.

There is an actual limit of 2000 imposed by the backend. If one tries to
save a project description longer than 2000 characters a warning will
appear after clicking `Save changes`.

Changelog: other