[cmake] drop -Wno-used-but-marked-unused

__attribute__((unused)) does emit that warning if a variable is used.
The C23/C++17 version [[maybe_unused]] does not, so drop the warning to
have consistency

cmake/CommonCompilerFlags.cmake

@@ -21,6 +21,7 @@ if(ENABLE_WARNING_VERBOSE)
       -Wno-reserved-identifier
       -Wno-covered-switch-default
       -Wno-disabled-macro-expansion
+      -Wno-used-but-marked-unused
     )
   endif()
 endif()