Update __git_flow_list_remote_features to use prefix config.
Update __git_flow_list_remote_features to use prefix config.

Use gitflow's feature prefix configuration option when fetching remote feature branches. This is used to determine which remote feature branches are available when completing 'feature track'.

thijsbekke/git-flow-completion,bjstar/git-flow-completion,petervanderdoes/git-flow-completion,ladyrassilon/git-hubflow-completion,bobthecow/git-flow-completion