test-mq-symlinks: fix symlink handling on solaris

It seems like ln -s gets confused if an existing symlink is dangling:
$ rm -f a b; ln -s a b; ln -sf b b
ln: cannot create b: File exists

We now rely on rm instead of on ln -sf.

tests/test-mq-symlinks

@@ -1,74 +1,75 b''
 #!/bin/sh
 
 "$TESTDIR/hghave" symlink || exit 80
 
 echo "[extensions]" >> $HGRCPATH
 echo "mq=" >> $HGRCPATH
 
 hg init
 hg qinit
 hg qnew base.patch
 echo aaa > a
 echo bbb > b
 echo ccc > c
 hg add a b c
 hg qrefresh
 $TESTDIR/readlink.py a
 
 echo '% test replacing a file with a symlink'
 hg qnew symlink.patch
 rm a
 ln -s b a
 hg qrefresh --git
 $TESTDIR/readlink.py a
 
 hg qpop
 hg qpush
 $TESTDIR/readlink.py a
 
 echo '% test updating a symlink'
 rm a
 ln -s c a
 hg qnew --git -f updatelink
 $TESTDIR/readlink.py a
 hg qpop
 hg qpush --debug
 $TESTDIR/readlink.py a
 hg st
 
 echo '% test replacing a symlink with a file'
 ln -s c s
 hg add s
 hg qnew --git -f addlink
 rm s
 echo sss > s
 hg qnew --git -f replacelinkwithfile
 hg qpop
 hg qpush
 cat s
 hg st
 
 echo '% test symlink removal'
 hg qnew removesl.patch
 hg rm a
 hg qrefresh --git
 hg qpop
 hg qpush
 hg st -c
 
 echo '% replace broken symlink with another broken symlink'
 ln -s linka linka
 hg add linka
 hg qnew link
 hg mv linka linkb
+rm linkb
 ln -sf linkb linkb
 hg qnew movelink
 hg qpop
 hg qpush
 $TESTDIR/readlink.py linkb
 echo '% check patch does not overwrite untracked symlinks'
 hg qpop
 ln -s linkbb linkb
 hg qpush
 
-true
  No newline at end of file
+true