Update links.md

Author: AngelaPastrana

docs/handbook/introduction/links.md

@@ -3,7 +3,6 @@
 The following important links are relevant to everyone who works in the lab:
 
 * **Lab website:** <http://learninglab.psych.purdue.edu>{target="_blank" rel="noreferrer"}
-* **Slack:** <https://learninglabpurdue.slack.com>{target="_blank" rel="noreferrer"}
 * **Google Calendars:** <https://calendar.google.com>{target="_blank" rel="noreferrer"}
 * **Sona:** <https://purdue-psych.sona-systems.com>{target="_blank" rel="noreferrer"}
 * **GitHub:** <https://github.com/PCLLAB/>{target="_blank" rel="noreferrer"}