build: Drop -Wno-unused-local-typedef

-Wunused-local-typedef(s) is covered by -Wunused in both gcc and clang.
No new warnings fire when compiling.

configure.ac

@@ -452,7 +452,6 @@ if test "x$CXXFLAGS_overridden" = "xno"; then
   dnl set the -Wno-foo case if it works.
   AX_CHECK_COMPILE_FLAG([-Wunused-parameter],[NOWARN_CXXFLAGS="$NOWARN_CXXFLAGS -Wno-unused-parameter"],,[[$CXXFLAG_WERROR]])
   AX_CHECK_COMPILE_FLAG([-Wself-assign],[NOWARN_CXXFLAGS="$NOWARN_CXXFLAGS -Wno-self-assign"],,[[$CXXFLAG_WERROR]])
-  AX_CHECK_COMPILE_FLAG([-Wunused-local-typedef],[NOWARN_CXXFLAGS="$NOWARN_CXXFLAGS -Wno-unused-local-typedef"],,[[$CXXFLAG_WERROR]])
   if test x$suppress_external_warnings != xyes ; then
     AX_CHECK_COMPILE_FLAG([-Wdeprecated-copy],[NOWARN_CXXFLAGS="$NOWARN_CXXFLAGS -Wno-deprecated-copy"],,[[$CXXFLAG_WERROR]])
   fi