configure.ac: remove AC_SEARCH_LIBS for libintl

This causes an additional dependency of mono on libintl which we didn't have before.
Reported by a user on gitter, it's problematic on macOS since it makes the mono binary depend on the libintl we ship in the Mono .pkg.

It was introduced in Mono 6.6 by https://github.com/mono/mono/commit/18e0ebfe89be0a175d2f904b9bb1ec6816daa318

src/mono/configure.ac

@@ -2947,13 +2947,6 @@ if test x$host_win32 = xno; then
 	AC_SEARCH_LIBS(shm_open, pthread rt posix4) 
 	AC_CHECK_FUNCS(shm_open)
 
-	dnl ********************************
-	dnl ***  Checks for gettext lib  ***
-	dnl ********************************
-	# This is needed for some hackery for AIX;
-	# Mono itself doesn't use it, but DllMap includes it
-	AC_SEARCH_LIBS([gettext], [intl])
-
 	dnl ********************************
 	dnl *** Checks for timezone stuff **
 	dnl ********************************