Fix dict_delete_get_min and max functions

[behrang]

I checked all functions in stdlib, and all of the functions that returns a boolean have a ? suffix, except for dict_delete_get_min and dict_delete_get_max functions, which together with udict and idict versions and modifying versions are a total of 12 functions.

Also removed :: from modifying versions of these functions since this was the only place in stdlib that they were used, and it makes them more similar to non-modifying versions.

It should not be a breaking change, since old users are using a copy of this stdlib and will not be affected, unless they update their library.