Convert the form builder
system_modules_uninstall() to a new-style Controller, using the instructions in the WSCCI Conversion Guide.
This issue also refactors the existing form to properly leverage ConfirmFormBase as a separate multi-step form step. Previously we only had a single form with a built-in switch for displaying the confirm form (which was bad). We are using a temporary (expirable) key value store entry for accomplishing this multi-step behavior. The tempstore is not used, because it also provides a lock, which is not wanted here.
PASSED: [[SimpleTest]]: [MySQL] 57,042 pass(es).
PASSED: [[SimpleTest]]: [MySQL] 56,933 pass(es).
PASSED: [[SimpleTest]]: [MySQL] 56,986 pass(es).