For not really obvious reasons, Sitecore doesn’t provide an intuitive way to remove a profile card or profile key added to a page. Once you assign it to the page, you don’t have a way to remove it.

One way to delete the profile card or profile key from a Sitecore item is to delete the assigned XML code directly from the item field. In order to do that, you need to follow the following steps:

• Step 1. Log in to Sitecore Desktop, then go to Content Editor.
• Step 2. Click on the red menu from the top left part of the browser window, then click on the Application Options, then check the following options:
• • From Show/Hide section, check the “Fields from the Standard template” option.
  • From Field values section, check the “Show raw values” option.

  The following image illustrates the Sitecore popup where the settings are located:
  

• Step 3. Go to the Sitecore item where the profile group or profile key is assigned, then go to the “Advanced” section and delete the value inside the “Tracking” field.
  
• Step 4. Revert the changes from Step 2 and you are done.

Hopefully Sitecore would add an easier way to remove the profile keys in the future. In case I am missing an easier option to do this, please let me know in the comments section.