Fix unnecessary ifdef when dealing with gettext

When adding support for gettext in #1070, a MacVim-specific ifdef was
added unnecessary around `bindtextdomain`. That ifdef isn't actually
necessary and it seems to have been done due to an incorrect
understanding of the ifdef logic there regarding `FEAT_GETTEXT`. Just
remove it to clean it up. Localization should still work.

Author: ychin

src/vim.h

@@ -571,11 +571,6 @@ extern int (*dyn_libintl_wputenv)(const wchar_t *envstring);
 # define _(x) ((char *)(x))
 # define NGETTEXT(x, xs, n) (((n) == 1) ? (char *)(x) : (char *)(xs))
 # define N_(x) x
-#ifdef FEAT_GUI_MACVIM
-    // In MacVim, we want bindtextdomain to work because we bundle the locale
-    // files in runtime dir instead of a global install loation. This is
-    // similar to Windows (which has DYNAMIC_GETTEXT set).
-#else
 # ifdef bindtextdomain
 #  undef bindtextdomain
 # endif
@@ -588,7 +583,6 @@ extern int (*dyn_libintl_wputenv)(const wchar_t *envstring);
 #  undef textdomain
 # endif
 # define textdomain(x) // empty
-#endif // MacVim
 #endif
 
 /*