Which repo is this ?
Take a look if the repo got deleted.. if yes.. add the repo and try to delete the tweak.
or try via Terminal
If you have Terminal installed, use dpkg -r full.package.name (use dpkg -l to find full.package.name)
You need openssh installed
another solution from reddit:
"Does this happen in No Substrate Mode? If so, you should attempt to reinstall Cydia Installer. If the problem persists, restore and rejailbreak (or run Cydia Impactor).
If it doesn't crash in No Substrate Mode, a tweak is causing the issue. Remove all recently installed tweaks. If the problem continues, remove Cydia Substrate (it will remove all tweaks). Now install your tweaks again one by one. Once Cydia crashes again, you can remove the last installed tweak."