chore: remove no-longer-needed backwards compatibility options

[kim-em]

No description provided.

[github-actions]

PR summary 0c08ce96d5

Import changes for modified files

No significant changes to the import graph

Import changes for all files

Files	Import difference

---

Declarations diff

No declarations were harmed in the making of this PR! 🐙

You can run this locally as follows

## summary with just the declaration names:
./scripts/declarations_diff.sh <optional_commit>

## more verbose report:
./scripts/declarations_diff.sh long <optional_commit>

The doc-module for scripts/declarations_diff.sh contains some details about this script.

---

Decrease in tech debt: (relative, absolute) = (125.99, 63.00)

Current number	Change	Type
11909	-47	backward.isDefEq
2	-126	backward.whnf

Current commit 70116177ba
Reference commit 0c08ce96d5

You can run this locally as

./scripts/technical-debt-metrics.sh pr_summary

• The relative value is the weighted sum of the differences with weight given by the inverse of the current value of the statistic.
• The absolute value is the relative value divided by the total sum of the inverses of the current values (i.e. the weighted average of the differences).