MNT: Build as `noarch: generic` so that conda doesn't do anything special with the bianca python scripts

The FSL Makefile system installs the bianca scripts into $PREFIX/bin/, but conda's special Python-specific processing rules were causing them to be moved into $PREFIX/python-scripts.

Something seems to have changed in how these files are processed, and with recent versions of conda, the final entry points are not being created in $PREFIX/bin/. I suspect that the non-standard #!/usr/bin/env fslpython hash-bang in bianca, and the fact that all of the other bianca scripts are #!/bin/bash scripts, may have something to do with this.