tcg: Remove outdated comments in helper-head.h

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

include/exec/helper-head.h

-/* Helper file for declaring TCG helper functions.
-   Used by other helper files.
-
-   Targets should use DEF_HELPER_N and DEF_HELPER_FLAGS_N to declare helper
-   functions.  Names should be specified without the helper_ prefix, and
-   the return and argument types specified.  3 basic types are understood
-   (i32, i64 and ptr).  Additional aliases are provided for convenience and
-   to match the types used by the C helper implementation.
-
-   The target helper.h should be included in all files that use/define
-   helper functions.  THis will ensure that function prototypes are
-   consistent.  In addition it should be included an extra two times for
-   helper.c, defining:
-    GEN_HELPER 1 to produce op generation functions (gen_helper_*)
-    GEN_HELPER 2 to do runtime registration helper functions.
+/*
+ * Helper file for declaring TCG helper functions.
+ * Used by other helper files.
  */
 
 #ifndef EXEC_HELPER_HEAD_H