Update function-schemata sub-module to HEAD (c9a98a1)

New changes:
1f5f95e definitions: [Z981] Correct to use argument references, not strings
928c0e8 Drop all PHP code and composer entry point, moved to WikiLambda
b4b6f6b Fix test to check data definitions validity
14f0453 Add test to check that all data definitions have their dependencies generated

Bug: T286975
Bug: T292093
Bug: T294920
Bug: T294944
Change-Id: I97c029a6e7696d3858d804b79da5c6985216b5da