Remove extraneous logic

Every version of Ruby released for at least the last decade was set to
use the -DRUBY19 flag. This commit sets the behavior in the flag as the
default.

Author: mhashizume

extconf.rb

@@ -7,13 +7,6 @@
 require 'mkmf'
 require 'rbconfig'
 
-$CFLAGS = case RUBY_VERSION
-          when /^1\.9/; '-DRUBY19'
-          when /^2\./; '-DRUBY19'
-          when /^3\./; '-DRUBY19'
-          else; ''
-          end
-
 implementation = case RbConfig::CONFIG['host_os']
                  when /linux/i; 'shadow'
                  when /sunos|solaris/i; 'shadow'
@@ -42,7 +35,7 @@
 
   if ok
     if !have_func("sgetspent")
-      $CFLAGS += ' -DSOLARIS'
+      $CFLAGS = '-DSOLARIS'
     end
   end
 when 'pwd'

pwd/shadow.c

@@ -23,11 +23,7 @@
 #include "rubyio.h"
 #endif
 
-#ifdef RUBY19
 #define file_ptr(x) (x)->stdio_file
-#else
-#define file_ptr(x) (x)->f
-#endif
 
 static VALUE rb_mShadow;
 static VALUE rb_mPasswd;

shadow/shadow.c

@@ -15,12 +15,7 @@
 #include "rubyio.h"
 #endif
 
-#ifdef RUBY19
 #define file_ptr(x) rb_io_stdio_file(x)
-#else
-#define file_ptr(x) (x)->f
-#endif
-
 #define NUM_FIELDS 10
 
 static VALUE rb_mShadow;