histedit: drop fallback to empty string from rendertemplate()
AFAICT, `cmdutil.rendertemplate()` always returns bytes (never
e.g. `None`), so we don't need to fall back to empty
(byte-)string. The fallback has been there since the code was added in
11c076786d56 (histedit: add templating support to histedit's rule file
generation, 2019-01-29).
Differential Revision: https://phab.mercurial-scm.org/D9244
phases: convert registernew users to use revision sets
Differential Revision: https://phab.mercurial-scm.org/D9233
phases: allow registration and boundary advancement with revision sets
The core internals either use revision sets already or can trivially use
them. Use the new interface in cg1unpacker.apply to avoid materializing
the list of all new nodes as it is normally just a revision range. This
avoids about 67 Bytes / changeset on AMD64 in peak RSS.
Differential Revision: https://phab.mercurial-scm.org/D9232