chore: Remove unused `/themes` folder #4505

Job	Run time
Check file changes	5s
Run React Tests	5m 23s
Build React App	4m 10s
Run Integration tests	5m 19s
E2E tests	9m 23s
Run API Tests	0s
Generate Hasura Change Summary	0s
Upsert Vultr Instance	18m 30s
Run Pulumi Preview	0s
Run Healthcheck on Pizza Services	59s
	43m 49s

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