largefiles: ignore removal status of files not managed in the target context

Before this patch, "hg status --rev REV" listed largefiles removed in
the working directory up with "R" mark, even if they aren't managed in
the REV. Normal files aren't listed up in such case.

When "lfilesrepo.status" is invoked for "hg status --rev REV", it
treats files on conditions below as "removed" (to avoid manifest full
scan in "ctx.status" ?):

  - marked as "R" in lfdirstate, or

  - files managed in the target revision but unknown in the manifest
    of the working context (= not including "R" files)

But the former can include files not managed in the target context.

To ignore removal status of files not managed in the target context,
this patch drops files unknown in the target revision from "removed"
list.

--HG--
branch : stable
largefiles: add examination of exec bit in "hg status --rev REV" case

Before this patch, "hg status --rev REV" doesn't list largefiles up
with "M" mark, even if exec bit of them is changed, because
"lfilesrepo.status" doesn't examine exec bit in such case.

--HG--
branch : stable