at-spi2-core: make introspection unconditional

We don't need to make it conditional anymore, this added line broke the gtk3 build.
With this the (cross) gtk3 build is working again.

pkgs/development/libraries/at-spi2-core/default.nix

@@ -58,7 +58,7 @@ stdenv.mkDerivation rec {
   doCheck = false;
 
   mesonFlags = [
-    "-Dintrospection=${if stdenv.buildPlatform == stdenv.hostPlatform then "yes" else "no"}"
+    "-Dintrospection=yes"
     # Provide dbus-daemon fallback when it is not already running when
     # at-spi2-bus-launcher is executed. This allows us to avoid
     # including the entire dbus closure in libraries linked with