Is there any way to remove an emblem?
There are currently no cards that explicitly remove emblems. The only way to get rid of an emblem is by activating the last loyalty ability on Karn Liberated. This restarts the game, and resets everything in the game except a specific set of cards that he keeps track of.

Mechanically, an emblem is intended to be a reward, in some sense, for completing a somewhat complicated process: casting a Planeswalker, adding to its loyalty for multiple turns, and then activating its expensive ability, all while keeping your opponent from messing up the plan. Because they are so hard to obtain, they are correspondingly difficult to remove. Some are easier to obtain, like the one from Gideon, Ally of Zendikar, but they are also weaker.