Removed implicit glfwMakeCurrentContext.

Implicitly making the context current makes sense in a
single-window API but less sense in a multi-window one.

tests/joysticks.c

@@ -196,6 +196,8 @@ int main(void)
     }
 
     glfwSetWindowSizeCallback(window_size_callback);
+
+    glfwMakeContextCurrent(window);
     glfwSwapInterval(1);
 
     while (!glfwGetWindowParam(window, GLFW_CLOSE_REQUESTED))