docs: Stop claiming to implement OpenVG

Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Reviewed-by: Christian Gmeiner <christian.gmeiner@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6500>
diff --git a/docs/systems.rst b/docs/systems.rst
index 334a766..087be90 100644
--- a/docs/systems.rst
+++ b/docs/systems.rst
@@ -7,7 +7,7 @@
 software drivers.
 
 The primary API is OpenGL but there's also support for OpenGL ES 1, ES2
-and ES 3, OpenVG, OpenCL, VDPAU, XvMC and the EGL interface.
+and ES 3, OpenCL, VDPAU, XvMC and the EGL interface.
 
 Hardware drivers include: