Removed implicit glfwMakeCurrentContext.

Implicitly making the context current makes sense in a
single-window API but less sense in a multi-window one.
diff --git a/tests/fsfocus.c b/tests/fsfocus.c
index e718a31..1c46d7a 100644
--- a/tests/fsfocus.c
+++ b/tests/fsfocus.c
@@ -91,7 +91,9 @@
         exit(EXIT_FAILURE);
     }
 
+    glfwMakeContextCurrent(window);
     glfwSwapInterval(1);
+
     glfwSetInputMode(window, GLFW_CURSOR_MODE, GLFW_CURSOR_NORMAL);
 
     glfwSetWindowFocusCallback(window_focus_callback);