Remove outdated conda_build.sh. (#4257)

This PR removes the `conda_build.sh` script from the repository root. This script appears to be outdated and unusable with the current cugraph recipes.

Authors:
  - Bradley Dice (https://github.com/bdice)

Approvers:
  - Ray Douglass (https://github.com/raydouglass)

URL: #4257