Why don't you just disable the network-manager service if you rely on wicd, and simply disable the autostart of nm-applet with:
$ sudo systemctl disable network-manager.service $ sudo echo "Hidden=true" >> /etc/xdg/autostart/nm-applet.desktop
You can also check your autostart configuration for .desktop files with dex in dry mode (you may need to sudo apt install dex first)
$ dex -ad ... Executing command: gsettings-data-convert Executing command: light-locker --late-locking Executing command: /usr/lib/gnome-settings-daemon/gsd-a11y-settings Executing command: /usr/lib/gnome-settings-daemon/gsd-color Executing command: /usr/lib/gnome-settings-daemon/gsd-datetime Executing command: /usr/lib/gnome-disk-utility/gsd-disk-utility-notify Executing command: /usr/lib/gnome-settings-daemon/gsd-housekeeping Executing command: /usr/lib/gnome-settings-daemon/gsd-keyboard Executing command: /usr/lib/gnome-settings-daemon/gsd-media-keys Executing command: /usr/lib/gnome-settings-daemon/gsd-power Executing command: /usr/lib/gnome-settings-daemon/gsd-print-notifications Executing command: /usr/lib/gnome-settings-daemon/gsd-rfkill Executing command: /usr/lib/gnome-settings-daemon/gsd-screensaver-proxy Executing command: /usr/lib/gnome-settings-daemon/gsd-sharing Executing command: /usr/lib/gnome-settings-daemon/gsd-smartcard Executing command: /usr/lib/gnome-settings-daemon/gsd-sound Executing command: /usr/lib/gnome-settings-daemon/gsd-wacom Executing command: /usr/lib/gnome-settings-daemon/gsd-wwan Executing command: /usr/lib/gnome-settings-daemon/gsd-xsettings ...
Unless you are proficient in configuring your wifi connection - including edits to the wpa_supplicant.conf for key-mgmt - from the terminal, you should definitely not mess with the network-manager's GUI wrapper nm-applet executable itself in /usr , because if for some reason your installation of wicd happens to break (user-error, accidentally, bug in an update etc.) you will still have all of your network-manager package files, including nm-applet GUI as a fallback, allowing you to apt update && apt [install/upgrade/full-upgrade]