I used the following procedure to safely remove the entire directory (YMMV):
1) Brought up Avast Premiere user interface
2) Clicked Gear icon in upper right
3) Selected Components
4) Turned "Antispam" OFF and selected Stop Permanently
5) To make sure all of the files aren't in use, Right Click on Avast tray icon, select Avast Shields Control, Disable until my computer is restarted
6) Delete the directory: "C:\ProgramData\AVAST Software\Avast\spamconf"
7) Once directory was completely deleted, I then restarted all of the disabled shields.
Re-enabling "all of the shields" meant that it restarted the Antispam under components, but the "spamconf" directory didn't immediately return. Not 100% sure why? Maybe someone a little more familiar with the application could bless this procedure for clearing out 2GB+ log files?