tests/test-execute-bit.t

rebase: delete seemingly unnecessary needupdate()

This seemed to be about checking that the user hasn't updated away
when we asked them to resolve merge conflicts. These days we call
`cmdutil.checkunfinished()` and refuse to update, so the user
shouldn't be able to get into this state.

`test-rebase-interruptions.t` actually has some tests where it
disables the rebase extension in order to be allowed to do some of
these updates. That still passes, but I wouldn't personally haved
cared if that failed.

Differential Revision: https://phab.mercurial-scm.org/D7825

#require execbit

  $ hg init
  $ echo a > a
  $ hg ci -Am'not executable'
  adding a

  $ chmod +x a
  $ hg ci -m'executable'
  $ hg id
  79abf14474dc tip

Make sure we notice the change of mode if the cached size == -1:

  $ hg rm a
  $ hg revert -r 0 a
  $ hg debugstate
  n   0         -1 unset               a
  $ hg status
  M a

  $ hg up 0
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg id
  d69afc33ff8a
  $ test -x a && echo executable -- bad || echo not executable -- good
  not executable -- good