dagutil: remove externalize() and externalizeall()
They are unused after the previous commit.
.. api:: externalize() and externalizeall() removed from dagutil
Use .node() on a storage primitive to perform revision to node
conversions.
Differential Revision: https://phab.mercurial-scm.org/D4305
#require docutils gettext
Error: the current ro localization has some rst defects exposed by
moving pager to core. These two warnings about references are expected
until the localization is corrected.
$ $TESTDIR/check-gendoc ro
checking for parse errors
gendoc.txt:58: (WARNING/2) Inline interpreted text or phrase reference start-string without end-string.
gendoc.txt:58: (WARNING/2) Inline interpreted text or phrase reference start-string without end-string.