glx: Remove GLXQueryContextInfoEXT fallback

GLX_EXT_libglvnd requires GLX 1.3, we can assume GLXQueryContext works.

src/GLX/libglx.c

@@ -388,18 +388,6 @@ static int __glXGetScreenForContextID(Display *dpy, __GLXdisplayInfo *dpyInfo,
         req->reqType = dpyInfo->glxMajorOpcode;
         req->glxCode = X_GLXQueryContext;
         req->context = contextID;
-    } else {
-        xGLXVendorPrivateReq *vpreq;
-        xGLXQueryContextInfoEXTReq *req;
-
-        GetReqExtra(GLXVendorPrivate,
-                sz_xGLXQueryContextInfoEXTReq - sz_xGLXVendorPrivateReq,
-                vpreq);
-        req = (xGLXQueryContextInfoEXTReq *) vpreq;
-        req->reqType = dpyInfo->glxMajorOpcode;
-        req->glxCode = X_GLXVendorPrivateWithReply;
-        req->vendorCode = X_GLXvop_QueryContextInfoEXT;
-        req->context = contextID;
     }
 
     _XReply(dpy, (xReply *) &reply, 0, False);