[delivery-service] drop dependency against scipy, install numpy using pip

[ccwienk]

Context / Motivation

scipy is used to calculate a function based on some data points. this is unnecessarily expensive and a very weird way of solving the problem of actually acquiring a function definition.

instead:

• define an equivalent function, and call it.
• then drop dependency to (then no longer) needed scipy package.

Also:

• install numpy using pip rather than alpine's package-mgr