[Cleanup] Remove deprecated environment variables

[romanc]

Description

PR #193 deprecated the following environment variables

• PACE_DACE_DEBUG
• PACE_LOGLEVEL
• PACE_FLOAT_PRECISION
• PACE_CONSTANTS

This issue is a reminder to remove the deprecated environment variables and re-simplify the logic for reading them.

Timeline

We need at least one released version of NDSL that allows reading the old and the new variables for the deprecation window to make sense. We can discuss working on this issue once we have a released version of NDSL including PR #193.