build: fix build without icu

When building without ICU (`vcbuild.bat intl-none`) the unicode/ucnv.h
header is not available, which causes compilation errors.

PR-URL: #14533
Reviewed-By: Timothy Gu <timothygu99@gmail.com>
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

src/node_i18n.h

@@ -25,7 +25,6 @@
 #if defined(NODE_WANT_INTERNALS) && NODE_WANT_INTERNALS
 
 #include "node.h"
-#include <unicode/ucnv.h>
 #include <string>
 
 #if defined(NODE_HAVE_I18N_SUPPORT)