wee_extension does its housekeeping in the directory 'installer' in the weewx user directory.
at some point you must have removed some of the housekeeping files that wee_extension installed. to fix it, remove the rest of the housekeeping files.
wee_extension will create the following in the weewx user directory (typically /home/weewx/bin/user or /usr/share/weewx/user, depending on how weewx itself was installed).
user/installer/
user/installer/EXTENSION_NAME/
user/installer/EXTENSION_NAME/install.py
you probably deleted user/installer/as3935/install.py but did not delete the directory user/installer/as3935
m