fix(renderer/generic): deinit render targets with framestate

This was a memory leak under Metal, leaked 1 swapchain worth of targets
every time a surface was closed.

Under OpenGL I think it was all cleaned up when the GL context was
destroyed.

src/renderer/generic.zig

@@ -395,6 +395,7 @@ pub fn Renderer(comptime GraphicsAPI: type) type {
             }
 
             pub fn deinit(self: *FrameState) void {
+                self.target.deinit();
                 self.uniforms.deinit();
                 self.cells.deinit();
                 self.cells_bg.deinit();