fix: import deprecate from @ember/debug

[ndekeister-us]

Same issue than the one on emberjs/ember-test-helpers#1066, in canary import { deprecate } from '@ember/application/deprecations' don't work anymore, replaced it by import { deprecate } from '@ember/debug';

When running test on ember-canary scenario, it is failing (job timeout) with this error

Global error: Uncaught Error: Could not find module `@ember/application/deprecations` imported from `dummy/initializers/flash-messages`

[ndekeister-us]

Hmm so ci/circleci:tests job is failing on this repo for canary scenario with this error

not ok 1 Chrome 92.0 - [undefined ms] - Global error: Uncaught Error: Could not find module `@ember/application/deprecations` imported from `@ember/test-helpers/setup-rendering-context` at http://localhost:7357/assets/vendor.js, line 259

...

Too long with no output (exceeded 10m0s): context deadline exceeded

It is (as funny as it sounds) the same issue linked on the PR description -> https://github.com/emberjs/ember-test-helpers/pull/1066/files

If i'm not wrong it is because, on this repo, @ember/test-helpers is added via ember-qunit@^4.6.0 dependencies and resolved to 1.7.x

We will also have to run ember-cli-update on https://github.com/poteto/ember-cli-flash/ so that it update to a recent version of ember, in which @ember/test-helpers have to be added as devDependencies to the project (see https://github.com/emberjs/ember-qunit/blob/master/docs/migration.md#qunit-and-embertest-helpers-dependencies)

[ndekeister-us]

Closing, will be done in #365