dirstate: Replace dropfile with drop_item_and_copy_source
Those removing a DirstateItem and a copy source are always done together
Differential Revision: https://phab.mercurial-scm.org/D11493
rust: Remove some obsolete doc-comments
About parameters that have been removed or replaced
Differential Revision: https://phab.mercurial-scm.org/D11492
dirstate: Remove return boolean from dirstatemap.dropfile
None of the remaining callers use it.
Differential Revision: https://phab.mercurial-scm.org/D11491