Remove unneeded _Fragment/VertexShaderPresent fields, update comments.
diff --git a/src/mesa/shader/shader_api.c b/src/mesa/shader/shader_api.c
index c439f71..70ceb70 100644
--- a/src/mesa/shader/shader_api.c
+++ b/src/mesa/shader/shader_api.c
@@ -199,8 +199,7 @@
 void
 _mesa_init_shader_state(GLcontext * ctx)
 {
-   ctx->Shader._FragmentShaderPresent = GL_FALSE;
-   ctx->Shader._VertexShaderPresent = GL_FALSE;
+   /* no-op */
 }