deskutils/calibre: Fix fetch

Grab mozilla-ca-certs.pem file from security/ca_root_nss instead
of fetching a changing file from the net. This avoids checksum
errors when the file is rerolled.

Reported by: pkg-fallout

(cherry picked from commit 2391c64feda2b0a2105d44eafb6dd1a59b2aaf9f)