[libc] newheadergen: removing extra .h (#99408)

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Differential Revision: https://phabricator.intern.facebook.com/D60251545

Author: aaryanshukla

libc/newhdrgen/yaml/wchar.yaml

@@ -4,7 +4,7 @@ types:
   - type_name: size_t
   - type_name: wint_t
   - type_name: wchar_t
-  - type_name: mbstate_t.h
+  - type_name: mbstate_t
 enums: []
 objects: []
 functions: