tests: drop a couple of unnecessary 'hghave symlink'

tests/test-manifest.t

@@ -1,5 +1,3 b''
-  $ "$TESTDIR/hghave" symlink || exit 80
-
 Source bundle was generated with the following script:
 
 # hg init

tests/test-merge-symlinks.t

@@ -1,5 +1,3 b''
-  $ "$TESTDIR/hghave" symlink || exit 80
-
   $ cat > echo.py <<EOF
   > #!/usr/bin/env python
   > import os, sys