[web] Do not try to rmtree symlinks in rmtreecontent()

There is a symlink in data directory (created by generate_static_dir() method)
and trying to rmtree() it will fail with an OSError. So we unlink() it
instead.

--HG--
branch : 3.25

cubicweb/web/webctl.py

@@ -44,7 +44,7 @@ def rmtreecontent(dst):
        itself)"""
     for fname in os.listdir(dst):
         fpath = osp.join(dst, fname)
-        if osp.isfile(fpath):
+        if osp.isfile(fpath) or osp.islink(fpath):
             os.unlink(fpath)
         else:
             rmtree(fpath)