Steam Mysteries of the Sith Uninstallation Guide
FIGURE 1 - Control Panel. Click Programs and Features.
FIGURE 2 - Programs and features. Click to select Jedi Knight: Dark Forces 2 and then click Uninstall.
FIGURE 3 - Steam will launch and you will receive the message "This will delete all Star Wars Jedi Knight Mysteries of the Sith game content from this computer". Click DELETE.
FIGURE 4 - Once deleted, your Steam game library will reflect the fact the game is not installed(See the INSTALL option is visible).