R1:f8e6240b9dfd

Move sprite sources from webroot/ to resources/

Summary:
- Since we'll never serve these directly, move them to resources/. This makes generating the Celerity map faster and reduces the size of the result map, since we don't need to analyze resources we'll never serve.
- Also Rename the 2x `subscribe-remove` to `subscribe-delete` since they were named inconsistently. Everything else is in good shape.

Test Plan: Generated sprites as per D4025

Reviewers: chad

Reviewed By: chad

CC: aran

Maniphest…