refactor(cli): remove destination-name forwarding shim

The separate-file decompression callback only reached the existing Rust
FIO_rust_determineDstName ABI through a two-argument C wrapper that supplied
the file-static suffix table and display string. Call the Rust ABI directly at
both decompression call sites, keeping the same suffix inputs and return-value
handling while removing the redundant wrapper and forward declaration.

Test Plan:
- `cc -fsyntax-only -Iprograms -Ilib -Ilib/common -Ilib/compress -Ilib/decompress -Ilib/dict -Ilib/legacy programs/fileio.c` -- passed.
- `git diff --check` and `git diff --cached --check` -- passed.
- Cargo, Make, native tests, fuzzers, and other heavy verification were not run
  per task constraints.

programs/fileio.c

@@ -4575,7 +4575,8 @@ typedef struct {
     const char* outDirName;
 } FIO_rust_decompress_multiple_separate_context_t;
 
-static const char* FIO_determineDstName(const char* srcFileName, const char* outDirName);
+static const char *suffixList[];
+static const char *suffixListStr;
 
 /* Keep destination-name construction, diagnostics, and private operations in
  * C; Rust owns per-file ordering and removal policy. */
@@ -4590,14 +4591,16 @@ static int FIO_rust_decompressMultipleSeparateFileCallback(void* opaque,
         char* validMirroredDirName = UTIL_createMirroredDestDirName(
             srcFileName, context->outMirroredRootDirName);
         if (validMirroredDirName) {
-            dstFileName = FIO_determineDstName(srcFileName, validMirroredDirName);
+            dstFileName = FIO_rust_determineDstName(
+                srcFileName, validMirroredDirName, suffixList, suffixListStr);
             free(validMirroredDirName);
         } else {
             DISPLAYLEVEL(2, "zstd: --output-dir-mirror cannot decompress '%s' into '%s'\n",
                          srcFileName, context->outMirroredRootDirName);
         }
     } else {
-        dstFileName = FIO_determineDstName(srcFileName, context->outDirName);
+        dstFileName = FIO_rust_determineDstName(
+            srcFileName, context->outDirName, suffixList, suffixListStr);
     }
 
     if (dstFileName == NULL) return 1;
@@ -4654,16 +4657,6 @@ static const char *suffixListStr =
 #endif
 ;
 
-/* FIO_determineDstName() :
- * create a destination filename from a srcFileName.
- * @return a pointer to it.
- * @return == NULL if there is an error */
-static const char*
-FIO_determineDstName(const char* srcFileName, const char* outDirName)
-{
-    return FIO_rust_determineDstName(srcFileName, outDirName, suffixList, suffixListStr);
-}
-
 int
 FIO_decompressMultipleFilenames(FIO_ctx_t* const fCtx,
                                 FIO_prefs_t* const prefs,