Remove unused metafield def owner type

[aswamy]

WHY are these changes introduced?

Doesn't look like brand being an owner type exists anymore when fetching metafield definitions: https://shopify.dev/docs/api/admin-graphql/2025-04/queries/metafieldDefinitions#argument-ownertype

We already removed it from os-web: https://github.com/Shopify/online-store-web/pull/21978/files

WHAT is this pull request doing?

• removed unused metafield owner type from code

How to test your changes?

n/a

Post-release steps

n/a

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

Checklist

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

[github-actions]

Coverage report

St.❔	Category	Percentage	Covered / Total
🟡	Statements	76.42%	9299/12169
🟡	Branches	71.65%	4559/6363
🟡	Functions	76.05%	2419/3181
🟡	Lines	76.98% (+0.01% 🔼)	8788/11416

Show files with reduced coverage 🔻

St.❔	File	Statements	Branches	Functions	Lines
🟢	... / app-event-watcher.ts	96.39% (-1.2% 🔻)	88.57% (-2.86% 🔻)	95.45%	100%

Test suite run success

2111 tests passing in 930 suites.

Report generated by 🧪jest coverage report action from 1163bb1