fix(cli): use public collision checker declaration

Rely on the existing fileio.h declaration now that the filename collision
checker is exported directly from Rust, avoiding a redundant C redeclaration
in the implementation file.

Test Plan: `ulimit -v 41943040; make -j1 -C tests test` passed; CLI lint and unit gates pending.

programs/fileio.c

@@ -320,7 +320,6 @@ int FIO_rust_multiFilesConcatAction(int nbFilesTotal,
 /* These policy and filesystem leaves are implemented by the Rust CLI archive.
  * The declarations in fileio.h remain the C ABI shims while file-I/O
  * orchestration and diagnostics stay here. */
-int FIO_checkFilenameCollisions(const char** filenameTable, unsigned nbFiles);
 /* FIO_highbit64() is a Rust-owned scalar policy leaf. */
 unsigned FIO_highbit64(unsigned long long v);
 unsigned long long FIO_getLargestFileSize(const char** inFileNames, unsigned nbFiles);