ext: drop IN_LIBXML and LIBXML_STATIC workarounds for windows

and the analogous workarounds for libxslt and libexslt

Author: flavorjones

ext/nokogiri/extconf.rb

@@ -924,10 +924,6 @@ def configure
       recipe.configure_options << "AR=/usr/bin/ar" unless ENV.key?("AR")
     end
 
-    if windows?
-      cflags = concat_flags(cflags, "-ULIBXML_STATIC", "-DIN_LIBXML")
-    end
-
     recipe.configure_options << if source_dir
       "--config-cache"
     else
@@ -965,11 +961,6 @@ def configure
       recipe.configure_options << "AR=/usr/bin/ar" unless ENV.key?("AR")
     end
 
-    if windows?
-      cflags = concat_flags(cflags, "-ULIBXSLT_STATIC", "-DIN_LIBXSLT")
-      cflags = concat_flags(cflags, "-ULIBEXSLT_STATIC", "-DIN_LIBEXSLT")
-    end
-
     recipe.configure_options << if source_dir
       "--config-cache"
     else