debian: Remove unused dependency on libproxy-dev by liblightwood-dev

liblightwood used libproxy before that code was removed for T2227.

Signed-off-by: Simon McVittie <smcv@collabora.com>
Reviewed-by: Justin Kim <justin.kim@collabora.com>
Differential Revision: https://phabricator.apertis.org/D6888

debian/control

@@ -61,7 +61,6 @@ Depends:
  libclutter-gst-3.0-dev,
  libglib2.0-dev,
  liblightwood-1-0 (= ${binary:Version}),
- libproxy-dev,
  libsoup-gnome2.4-dev,
  libthornbury-dev (>=0.1703.0),
  ${misc:Depends},