Change default settings to not leave segments

[counsyl-opensource]

Even though it's better for performance to not check for segments if we know we are just going to be deleting whole directories, ultimately you should opt-in to leaving segments - otherwise it's overly surprising for interactive use.

Should be one-line change + some changes within-Counsyl.

cc @krhaas @wesleykendall

[counsyl-opensource]

(whoops this was @jtratner under wrong username)