tests/test-hgk.t

merge: remove last traces of fastforward merging

bbc97d419b16 introduced fast-forward branch merging.
66ed92ed115a partly removed it again.

The fastforward variable would always be false if branchmerge was false, so the
fastforward variable makes no difference and we can remove it completely.

Minimal hgk check

  $ echo "[extensions]" >> $HGRCPATH
  $ echo "hgk=" >> $HGRCPATH
  $ hg init repo
  $ cd repo
  $ echo a > a
  $ hg ci -Am adda
  adding a
  $ hg debug-cat-file commit 0
  tree a0c8bcbbb45c
  parent 000000000000
  author test 0 0
  committer test 0 0
  revision 0
  branch default
  
  adda