repository: remove candelta() from ifileindex
candelta() was previously called by changegroup code. With delta
generation moved to the storage API, there are no more external
consumers of this method and it can be removed from the storage
interface.
Differential Revision: https://phab.mercurial-scm.org/D4236
$ hg init
$ echo a > a
$ hg ci -Am t
adding a
$ hg mv a b
$ hg ci -Am t1
$ hg debugrename b
b renamed from a:b789fdd96dc2f3bd229c1dd8eedf0fc60e2b68e3
$ hg mv b a
$ hg ci -Am t2
$ hg debugrename a
a renamed from b:37d9b5d994eab34eda9c16b195ace52c7b129980
$ hg debugrename --rev 1 b
b renamed from a:b789fdd96dc2f3bd229c1dd8eedf0fc60e2b68e3