Kizume and Rhm Zanz it should be still there as that is what manages that specific feature.
In the top menu bar, where is says: Finder File Edit View Go Windows Help
Click on the Go, and in the same time click the option key on your keyboard near the space bar. In that the drop down menu list the word Library will appear.
Click on Library and Finder will open, look for the Preferences folder. Within that folder which should be in alphabetical order look for the file named, com.apple.sharekit.recents.plist
Drag that file out of finder and unto your desktop. Close out the Finder window and close out all other your applications, including Safari, and reboot your Mac and once it turns on, reopen Safari and look at your share sheet. Any recents should be gone. That file named com.apple.sharekit.recents.plist will recreate itself on a clean slate in that folder. Should you encounter that you shared something again to a contact with Safari's share sheet, be sure to follow the same directions.
Cheers!