Remove "Alexa Top Sites Captcha and Tor Block Monitoring" from GSOC project ideas

Remove it from here: https://community.torproject.org/gsoc/

This project was taken up in GSOC 2021 by woswos and ranchak. Here is their final report: https://gitlab.torproject.org/woswos/CAPTCHA-Monitor/-/wikis/GSoC-2021/Final-Report