build: Remove -Wno-unused-value from default CXXFLAGS

The ncurses bug (#542031) has long been fixed.

m4/dpkg-compiler.m4

@@ -17,8 +17,7 @@ WFLAGS="-Wall -Wextra -Wno-unused-parameter -Wno-missing-field-initializers \
 	 -Wvla -Winit-self -Wwrite-strings -Wcast-align -Wshadow"
 WCFLAGS="-Wdeclaration-after-statement -Wnested-externs -Wbad-function-cast \
 	 -Wstrict-prototypes -Wmissing-prototypes -Wold-style-definition"
-# Temporarily here until #542031 gets fixed in ncurses
-WCXXFLAGS="-Wno-unused-value"
+WCXXFLAGS=""
 if test "x$enable_compiler_warnings" = "xyes"; then
 	if test "x$GCC" = "xyes"; then
 		CFLAGS="$WFLAGS $WCFLAGS $CFLAGS"