Remove `future_t=0` predictions from `expected_customer_lifetime_value` function

[ColtAllen]

expected_customer_lifetime_value is essentially a FOR loop across the specified time range, and it is initialized with an array of zeroes. However, instead of simply creating an array of zeros, model predictions are being ran for zero time periods into the future. Not only is this inefficient, but it's also raising DIV/0 warnings for some transaction models because it's a nonsensical parameter specification. Initializing with the array of zeroes also may not even be required at all.