flex: use the new gettext logic

This commit switches to use the new gettext logic, which involves:

 - using TARGET_NLS_DEPENDENCIES instead of hand-encoded dependencies
   on gettext/host-gettext

 - dropping BR2_PACKAGE_GETTEXT selection

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/flex/Config.in

@@ -1,6 +1,5 @@
 config BR2_PACKAGE_FLEX
 	bool "flex"
-	select BR2_PACKAGE_GETTEXT if BR2_NEEDS_GETTEXT_IF_LOCALE
 	help
 	  A fast lexical analyser generator. A tool for generating
 	  programs that perform pattern-matching on text.

package/flex/flex.mk

@@ -9,8 +9,7 @@ FLEX_SITE = https://github.com/westes/flex/files/981163
 FLEX_INSTALL_STAGING = YES
 FLEX_LICENSE = FLEX
 FLEX_LICENSE_FILES = COPYING
-FLEX_DEPENDENCIES = \
-	$(if $(BR2_PACKAGE_GETTEXT_IF_LOCALE),gettext) host-m4
+FLEX_DEPENDENCIES = $(TARGET_NLS_DEPENDENCIES) host-m4
 FLEX_CONF_ENV = ac_cv_path_M4=/usr/bin/m4
 HOST_FLEX_DEPENDENCIES = host-m4