Catalysis of the reaction: L-2-amino-4-chloropent-4-enoate + H2O = 2-oxopent-4-enoate + chloride + H+ + NH4.
L-2-amino-4-chloropent-4-enoate chloride-lyase (adding H2O; deaminating; 2-oxopent-4-enoate-forming)