GNOME - How to remove app launchers from the activities menu
App launchers shown in GNOME Activities are located either in /usr/share/applications/ or ~/.local/share/applications/ as .desktop files.
You can hide an individual app launcher from Activities by adding an extra NoDisplay=true line to the corresponding .desktop file.
It is generally not advisable to edit the .desktop file located in /usr/share/applications/. Instead copy the file to ~/.local/share/applications/ first and make the change to the copied file.
If you can't find the right .desktop file in any of the two locations mentioned above, try /usr/local/share/applications too.
The GUI way could be to install "Alacarte". It's super easy to manage and remove app launchers from the menu.