Remove constraints unnecessary since buster

* Build-Depends: Drop versioned constraint on libcurl4-gnutls-dev, libxml2-dev, libyaml-dev and qtbase5-dev.
* libappstream-dev: Drop versioned constraint on libglib2.0-dev in Depends.
* libappstreamqt-dev: Drop versioned constraint on qtbase5-dev in Depends.

Changes-By: deb-scrub-obsolete