* Revert "Add dashing config file for generating docset from flutter docs (#24374)"

This reverts commit ec8ca860.

* Revert "Update driver script to execute test through test_core (#24168)"

This reverts commit 6c62cf33.

This reverts commit 71e9bd6f.

* Upgrade everything except matcher.
* Roll matcher (and test)
* Adjust tests that depend on flutter:test directly to depend on a shim
* Require use of package:test shim and remove other references to package:test