st/vega: Remove.

OpenVG API seems to have dwindled away.  The code
would still be interesting if we wanted to implement NV_path_rendering
but given the trend of the next gen graphics APIs, it seems
unlikely that this becomes ARB or core.

v2: Remove a few "openvg" references left, per Emil Velikov.

Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>

v3: Update release notes.

docs/relnotes/10.6.0.html

@@ -61,6 +61,7 @@ TBD.
 <ul>
 <li>Removed classic Windows software rasterizer.</li>
 <li>Removed egl_gallium EGL driver.</li>
+<li>Removed OpenVG support.</li>
 </ul>
 
 </div>

docs/relnotes/7.6.html

@@ -48,7 +48,7 @@ c49c19c2bbef4f3b7f1389974dff25f4  MesaGLUT-7.6.zip
 
 <h2>New features</h2>
 <ul>
-<li><a href="../openvg.html">OpenVG</a> front-end (state tracker for Gallium).
+<li>OpenVG front-end (state tracker for Gallium).
 This was written by Zack Rusin at Tungsten Graphics.
 <li>GL_ARB_vertex_array_object and GL_APPLE_vertex_array_object extensions
     (supported in Gallium drivers, Intel DRI drivers, and software drivers)</li>