test: fix invalid redirection for histedit text

Appending to the file is wrong, we want new content.

tests/test-histedit-obsolete.t

@@ -1,142 +1,142 b''
   $ . "$TESTDIR/histedit-helpers.sh"
 
 Enable obsolete
 
   $ cat > ${TESTTMP}/obs.py << EOF
   > import mercurial.obsolete
   > mercurial.obsolete._enabled = True
   > EOF
 
   $ cat >> $HGRCPATH << EOF
   > [ui]
   > logtemplate= {rev}:{node|short} {desc|firstline}
   > [phases]
   > publish=False
   > [extensions]'
   > histedit=
   > 
   > obs=${TESTTMP}/obs.py
   > EOF
 
   $ hg init base
   $ cd base
 
   $ for x in a b c d e f ; do
   >     echo $x > $x
   >     hg add $x
   >     hg ci -m $x
   > done
 
   $ hg log --graph
   @  5:652413bf663e f
   |
   o  4:e860deea161a e
   |
   o  3:055a42cdd887 d
   |
   o  2:177f92b77385 c
   |
   o  1:d2ae7f538514 b
   |
   o  0:cb9a9f314b8b a
   
 
   $ HGEDITOR=cat hg histedit 1
   pick d2ae7f538514 1 b
   pick 177f92b77385 2 c
   pick 055a42cdd887 3 d
   pick e860deea161a 4 e
   pick 652413bf663e 5 f
   
   # Edit history between d2ae7f538514 and 652413bf663e
   #
   # Commands:
   #  p, pick = use commit
   #  e, edit = use commit, but stop for amending
   #  f, fold = use commit, but fold into previous commit (combines N and N-1)
   #  d, drop = remove commit from history
   #  m, mess = edit message without changing commit content
   #
   0 files updated, 0 files merged, 0 files removed, 0 files unresolved
-  $ cat >> commands.txt <<EOF
+  $ cat > commands.txt <<EOF
   > pick 177f92b77385 2 c
   > drop d2ae7f538514 1 b
   > pick 055a42cdd887 3 d
   > fold e860deea161a 4 e
   > pick 652413bf663e 5 f
   > EOF
   $ hg histedit 1 --commands commands.txt --verbose | grep histedit
   saved backup bundle to $TESTTMP/base/.hg/strip-backup/34a9919932c1-backup.hg (glob)
   $ hg log --graph --hidden
   @  8:0efacef7cb48 f
   |
   o  7:ae467701c500 d
   |
   o  6:d36c0562f908 c
   |
   | x  5:652413bf663e f
   | |
   | x  4:e860deea161a e
   | |
   | x  3:055a42cdd887 d
   | |
   | x  2:177f92b77385 c
   | |
   | x  1:d2ae7f538514 b
   |/
   o  0:cb9a9f314b8b a
   
   $ hg debugobsolete
   e860deea161a2f77de56603b340ebbb4536308ae ae467701c5006bf21ffcfdb555b3d6b63280b6b7 0 {'date': '*', 'user': 'test'} (glob)
   652413bf663ef2a641cab26574e46d5f5a64a55a 0efacef7cb481bf574f69075b82d044fdbe5c20f 0 {'date': '*': 'test'} (glob)
   d2ae7f538514cd87c17547b0de4cea71fe1af9fb 0 {'date': '*', 'user': 'test'} (glob)
   055a42cdd88768532f9cf79daa407fc8d138de9b ae467701c5006bf21ffcfdb555b3d6b63280b6b7 0 {'date': '*': 'test'} (glob)
   177f92b773850b59254aa5e923436f921b55483b d36c0562f908c692f5204d606d4ff3537d41f1bf 0 {'date': '*', 'user': 'test'} (glob)
 
 Ensure hidden revision does not prevent histedit
 -------------------------------------------------
 
 create an hidden revision
 
   $ cat > commands.txt <<EOF
   > pick d36c0562f908 6 c
   > drop ae467701c500 7 d
   > pick 0efacef7cb48 8 f
   > EOF
   $ hg histedit 6 --commands commands.txt
   0 files updated, 0 files merged, 3 files removed, 0 files unresolved
   0 files updated, 0 files merged, 0 files removed, 0 files unresolved
   $ hg log --graph
   @  9:7c044e3e33a9 f
   |
   o  6:d36c0562f908 c
   |
   o  0:cb9a9f314b8b a
   
 check hidden revision are ignored (6 have hidden children 7 and 8)
 
   $ cat > commands.txt <<EOF
   > pick d36c0562f908 6 c
   > pick 7c044e3e33a9 8 f
   > EOF
   $ hg histedit 6 --commands commands.txt
   0 files updated, 0 files merged, 0 files removed, 0 files unresolved
 
 
 Check that histedit respect phases
 =========================================
 
 (not directly related to the test file but doesn't deserve it's own test case)
 
   $ hg log -G
   @  9:7c044e3e33a9 f
   |
   o  6:d36c0562f908 c
   |
   o  0:cb9a9f314b8b a
   
   $ hg ph -pv '.^'
   phase changed for 2 changesets
   $ hg histedit -r '.~2'
   abort: cannot edit immutable changeset: cb9a9f314b8b
   [255]