This command removes the spell (or power, shout, disease, etc) with the specified ID from your current target. Use 'player.removespell' to remove a spell from your own character.
removespell [spell id] Target Command
|Spell ID||The ID of the spell you wish to remove from your target.|
"Conjure Familiar" has a spell ID of 000640B6. This command would remove the spell Conjure Familiar from your target.
"Conjure Dragon Priest" has a spell ID of 0010FC16. This command would remove the spell Conjure Dragon Priest from your character (not your target).