Remove Quantopian logo

the website is down, company is defunct since 2020
(https://en.wikipedia.org/wiki/Quantopian)

Author: krassowski

assets/logos/quantopian.svg

@@ -229,9 +229,6 @@
     - href: https://www.oreilly.com
       src: oreilly.svg
       alt: OReilly
-    - href: https://www.quantopian.com
-      src: quantopian.svg
-      alt: Quantopian
     - href: https://quantstack.net
       src: quantstack.svg
       alt: QuantStack