ci: Remove Dockerfile as it is replaced by new logic

.gitlab-ci/Dockerfile

@@ -1,36 +0,0 @@
-# Rebuild and push with
-#
-#  cd .gitlab-ci/
-#  docker build --no-cache -t registry.freedesktop.org/libfprint/libfprint/master:v1 .
-#  docker push registry.freedesktop.org/libfprint/libfprint/master:v1
-#
-
-FROM fedora:rawhide
-
-RUN dnf -y update && dnf -y upgrade && \
-  dnf -y install \
-         doxygen \
-         flatpak-builder \
-         gcc \
-         gcc-c++ \
-         git \
-         glib2-devel \
-         glibc-devel \
-         gobject-introspection-devel \
-         gtk-doc \
-         gtk3-devel \
-         libabigail \
-         libgusb-devel \
-         libX11-devel \
-         libXv-devel \
-         meson \
-         nss-devel \
-         pixman-devel \
-         python3-cairo \
-         python3-gobject \
-         systemd \
-         umockdev \
-         uncrustify \
-         valgrind \
-  && \
-  dnf clean all