Remove legacy app schema

[gonzaloriestra]

WHY are these changes introduced?

⚠️ These PRs for the templates must be merged first (the acceptance tests will pass then):

• https://github.com/Shopify/shopify-app-template-react-router/pull/127
• https://github.com/Shopify/shopify-app-template-none/pull/24

The subscriptions-reference-app template is ready, and I guess there's no need to update old templates like Remix, Node, Ruby or PHP templates.

Fixes #0000

WHAT is this pull request doing?

How to test your changes?

Post-release steps

Measuring impact

How do we know this change was effective? Please choose one:

• [ ] n/a - this doesn't need measurement, e.g. a linting rule or a bug-fix
• [ ] Existing analytics will cater for this addition
• [ ] PR includes analytics changes to measure impact

Checklist

• [ ] I've considered possible cross-platform impacts (Mac, Linux, Windows)
• [ ] I've considered possible documentation changes

[github-actions[bot]]

Coverage report

St.:grey_question:	Category	Percentage	Covered / Total
🟡	Statements	79.26% (+0.03% 🔼)	13564/17114
🟡	Branches	73.14% (+0.03% 🔼)	6610/9038
🟡	Functions	79.34% (-0.03% 🔻)	3502/4414
🟡	Lines	79.61% (+0.03% 🔼)	12813/16094

Show files with reduced coverage 🔻

St.:grey_question:	File	Statements	Branches	Functions	Lines
🟢	... / app.test-data.ts	91.88% (-0.16% 🔻)	94.59% (+0.68% 🔼)	82.35% (-0.21% 🔻)	91.26% (-0.19% 🔻)
🟢	... / app.ts	88.02% (+1.39% 🔼)	68.97% (+0.39% 🔼)	93.33% (-0.32% 🔻)	88.59% (+0.25% 🔼)
🟢	... / loader.ts	93.15% (-0.71% 🔻)	84.66% (-2.17% 🔻)	97.06%	93.65% (-1.02% 🔻)
🟢	... / common.ts	87.5% (-12.5% 🔻)	88.89% (-11.11% 🔻)	100%	100%
🟢	... / app-context.ts	96.55% (-0.11% 🔻)	89.47% (-1.83% 🔻)	100%	96.43% (-0.12% 🔻)
🔴	... / dev.ts	16.54% (-0.65% 🔻)	16.44% (-0.89% 🔻)	19.44%	16.95% (-0.7% 🔻)
🟢	... / link.ts	96.34% (-0.17% 🔻)	95.16% (-0.29% 🔻)	100%	96.15% (-0.19% 🔻)
🟢	... / ConcurrentOutput.tsx	98.36% (-1.64% 🔻)	92% (-4% 🔻)	100%	98.33% (-1.67% 🔻)
🟢	... / string.ts	93.22% (-1.69% 🔻)	79.17% (-4.17% 🔻)	95.65%	96.08%
🔴	... / dev.ts	13.04% (-0.29% 🔻)	2.94%	57.14%	13.04% (-0.29% 🔻)
🟢	... / theme-uploader.ts	91.84% (+0.12% 🔼)	78.21% (-0.83% 🔻)	86.36% (-1.14% 🔻)	93.18% (+0.59% 🔼)
🟡	... / theme-environment.ts	70.45% (-0.97% 🔻)	50%	57.89% (-0.93% 🔻)	70.45% (-0.97% 🔻)

Test suite run success

3347 tests passing in 1371 suites.

Report generated by 🧪jest coverage report action from 3cc6b58f20749ae9c400ada05a2b86be1ea54306