tests: remove third head in some of the 'rebase-parameters' tests

tests: remove third head in some of the 'rebase-parameters' tests

These tests do not care about that extra branch at all. In future changeset we
will make rebase behave like merge and abort in case of an ambiguous destination
(eg: multiple other heads) and that extra branch will make the command
invocation breaks.

We preventively remove this extra branch from the relevant tests in an
independant changeset to reduce noise and increase confidence in the final
change.

--- a/tests/test-rebase-parameters.t	Sun Feb 07 15:21:39 2016 +0900
+++ b/tests/test-rebase-parameters.t	Mon Feb 08 14:02:53 2016 +0100
@@ -46,11 +46,14 @@
   
   $ cd ..
 
+Version with only two heads (to allow default destination to work)
+
+  $ hg clone -q -u . a a2heads -r 3 -r 8
 
 These fail:
 
-  $ hg clone -q -u . a a1
-  $ cd a1
+  $ hg clone -q -u . a a0
+  $ cd a0
 
   $ hg rebase -s 8 -d 7
   nothing to rebase
@@ -117,6 +120,9 @@
 
 Rebase with no arguments (from 3 onto 8):
 
+  $ cd ..
+  $ hg clone -q -u . a2heads a1
+  $ cd a1
   $ hg up -q -C 3
 
   $ hg rebase
@@ -126,22 +132,18 @@
   saved backup bundle to $TESTTMP/a1/.hg/strip-backup/42ccdea3bb16-3cb021d3-backup.hg (glob)
 
   $ hg tglog
-  @  8: 'D'
-  |
-  o  7: 'C'
+  @  6: 'D'
   |
-  o  6: 'B'
+  o  5: 'C'
   |
-  o  5: 'I'
+  o  4: 'B'
   |
-  o  4: 'H'
+  o  3: 'I'
   |
-  | o  3: 'G'
-  |/|
-  o |  2: 'F'
-  | |
-  | o  1: 'E'
-  |/
+  o  2: 'H'
+  |
+  o  1: 'F'
+  |
   o  0: 'A'
   
 Try to rollback after a rebase (fail):
@@ -154,7 +156,7 @@
 
 Rebase with base == '.' => same as no arguments (from 3 onto 8):
 
-  $ hg clone -q -u 3 a a2
+  $ hg clone -q -u 3 a2heads a2
   $ cd a2
 
   $ hg rebase --base .
@@ -164,22 +166,18 @@
   saved backup bundle to $TESTTMP/a2/.hg/strip-backup/42ccdea3bb16-3cb021d3-backup.hg (glob)
 
   $ hg tglog
-  @  8: 'D'
-  |
-  o  7: 'C'
+  @  6: 'D'
   |
-  o  6: 'B'
+  o  5: 'C'
   |
-  o  5: 'I'
+  o  4: 'B'
   |
-  o  4: 'H'
+  o  3: 'I'
   |
-  | o  3: 'G'
-  |/|
-  o |  2: 'F'
-  | |
-  | o  1: 'E'
-  |/
+  o  2: 'H'
+  |
+  o  1: 'F'
+  |
   o  0: 'A'
   
   $ cd ..
@@ -220,7 +218,7 @@
 
 Specify only source (from 2 onto 8):
 
-  $ hg clone -q -u . a a4
+  $ hg clone -q -u . a2heads a4
   $ cd a4
 
   $ hg rebase --source 'desc("C")'
@@ -229,20 +227,16 @@
   saved backup bundle to $TESTTMP/a4/.hg/strip-backup/5fddd98957c8-f9244fa1-backup.hg (glob)
 
   $ hg tglog
-  o  8: 'D'
+  o  6: 'D'
   |
-  o  7: 'C'
-  |
-  @  6: 'I'
+  o  5: 'C'
   |
-  o  5: 'H'
+  @  4: 'I'
   |
-  | o  4: 'G'
-  |/|
-  o |  3: 'F'
-  | |
-  | o  2: 'E'
-  |/
+  o  3: 'H'
+  |
+  o  2: 'F'
+  |
   | o  1: 'B'
   |/
   o  0: 'A'
@@ -285,7 +279,7 @@
 
 Specify only base (from 1 onto 8):
 
-  $ hg clone -q -u . a a6
+  $ hg clone -q -u . a2heads a6
   $ cd a6
 
   $ hg rebase --base 'desc("D")'
@@ -295,22 +289,18 @@
   saved backup bundle to $TESTTMP/a6/.hg/strip-backup/42ccdea3bb16-3cb021d3-backup.hg (glob)
 
   $ hg tglog
-  o  8: 'D'
-  |
-  o  7: 'C'
+  o  6: 'D'
   |
-  o  6: 'B'
+  o  5: 'C'
   |
-  @  5: 'I'
+  o  4: 'B'
   |
-  o  4: 'H'
+  @  3: 'I'
   |
-  | o  3: 'G'
-  |/|
-  o |  2: 'F'
-  | |
-  | o  1: 'E'
-  |/
+  o  2: 'H'
+  |
+  o  1: 'F'
+  |
   o  0: 'A'
   
   $ cd ..
@@ -383,7 +373,7 @@
 
 Specify only revs (from 2 onto 8)
 
-  $ hg clone -q -u . a a9
+  $ hg clone -q -u . a2heads a9
   $ cd a9
 
   $ hg rebase --rev 'desc("C")::'
@@ -392,20 +382,16 @@
   saved backup bundle to $TESTTMP/a9/.hg/strip-backup/5fddd98957c8-f9244fa1-backup.hg (glob)
 
   $ hg tglog
-  o  8: 'D'
+  o  6: 'D'
   |
-  o  7: 'C'
-  |
-  @  6: 'I'
+  o  5: 'C'
   |
-  o  5: 'H'
+  @  4: 'I'
   |
-  | o  4: 'G'
-  |/|
-  o |  3: 'F'
-  | |
-  | o  2: 'E'
-  |/
+  o  3: 'H'
+  |
+  o  2: 'F'
+  |
   | o  1: 'B'
   |/
   o  0: 'A'