Remove Open Collective postinstall script to fix deno installation warning

[Balearica]

We currently have a postinstall script that prints a message telling people they can donate to support development. Using postinstall scripts for this purpose was common at the time this was added, however this has since fallen out of favor for a number of reasons, and is no longer recommended by Open Collective (see this issue).

More concerningly, deno prints a warning that makes it unclear whether the package has installed correctly or not. To avoid confusion, we should switch to whatever the current best practice is for this.

Warning The following packages contained npm lifecycle scripts (preinstall/install/postinstall) that were not executed:
┠─ npm:@scribe.js/tesseract.js@6.0.2
┃
┠─ This may cause the packages to not work correctly.
┖─ To run lifecycle scripts, use the `--allow-scripts` flag with `deno install`:
   deno install --allow-scripts=npm:@scribe.js/tesseract.js@6.0.2