Does removing First Strike affect creatures with Double strike?
No.  First Strike and Double Strike are entirely separate abilities.

First Strike and Double Strike are different abilities with overlap in their effects.  Effects that care about First Strike ignore Double Strike, and vis versa.

From the rulings on Urborg (which has the ability "{T}: Target creature loses first strike or swampwalk until end of turn."):


  Urborg’s second ability affects only the first strike ability, not the part of the double strike ability that acts like first strike.