[scudo] Remove internal linkage from LargeBlock header helpers (NFC) (#207708)

`addHeaderTag` and `getHeader` are static function templates in
`secondary.h,` so any TU that includes the header without using them
trips `-Wunused-template`. Dropping static fixes the warning.

Part of #202945.

GitOrigin-RevId: dcf969eaf2c25048542d13946ca5ff65be5bc7ab
1 file changed