[Clang][perf-training] Fix clean command in perf-helper.py

The first path argument was always being ignored, and since most
calls to this command only passed one path, it wasn't actually doing
anything in most cases.

Author: tstellar

clang/utils/perf-training/perf-helper.py

@@ -36,7 +36,7 @@ def clean(args):
             + "\tRemoves all files with extension from <path>."
         )
         return 1
-    for path in args[1:-1]:
+    for path in args[0:-1]:
         for filename in findFilesWithExtension(path, args[-1]):
             os.remove(filename)
     return 0