[FT] Remove obsolete config properties (frozen, output_regex)

[hynky1999]

Request

Removed obselete config properties:

• frozen
• output_regex

For more context see:
#289

the output_regex is legacy from the harness, we needed it for bigbench tasks but this is now handled by the metrics direclty. Frozen was to make sure the task did not change over time but we are now using task versioning for this.

[clefourrier]

Agree on both.
Note: frozen was initially for tasks that we had thoroughly debugged and that were included in the test suite, hence that were not expected to change definition as they were robust. So it's also an indicator of higher quality.