syntax: makefile: ensure that the <Tab> key always produces a tab

Making it independent from the `tabstospaces` setting.

And remove the now-redundant suggestion from the sample nanorc.

doc/sample.nanorc.in

@@ -260,9 +260,6 @@
 ## independent of the settings of 'tabsize' and 'tabstospaces':
 # extendsyntax python tabgives "    "
 
-## If <Tab> should always produce an actual TAB when editing a Makefile:
-# extendsyntax makefile tabgives "	"
-
 
 ## === Key bindings ===
 ## For all details, see 'man nanorc', section REBINDING KEYS.

syntax/makefile.nanorc

@@ -2,6 +2,8 @@
 
 syntax makefile "(/((GNU)?m|M)akefile[^/]*$|\.(make|mk)$)"
 magic "makefile script"
+
+tabgives "	"
 comment "#"
 
 # Assignments.