revlog: simplify rawtext return value
We're always returning a tuple even though only the raw text is being used,
and we're rebuilding another tuple again higher.
As a bonus, this will remove one tuple creation and deletion
per `raw_text` call, hence fewer gc calls, etc.
#if no-windows
$ mkdir -p xdgconf/hg
$ echo '[ui]' > xdgconf/hg/hgrc
$ echo 'username = foobar' >> xdgconf/hg/hgrc
$ XDG_CONFIG_HOME="`pwd`/xdgconf" ; export XDG_CONFIG_HOME
$ unset HGRCPATH
$ hg config ui.username 2>/dev/null
foobar
#endif