If you installed with package control, search for “Package Control: Remove Package” in the command palette (accessed with Ctrl+Shift+P). Otherwise you can just remove the Emmet directory.
If you wish to use a custom caption to access commands, create Default.sublime-commands in your User folder. Then insert something similar to the following.
[
{
"caption": "Package Control: Uninstall Package",
"command": "remove_package"
}
]
Of course, you can customize the command and caption as you see fit.