util: move "default" unlinkpath to posix.py

we have a unlinkpath in windows.py

mercurial/posix.py

@@ -328,3 +328,13 b' def termwidth():'
 
 def makedir(path, notindexed):
     os.mkdir(path)
+
+def unlinkpath(f):
+    """unlink and remove the directory if it is empty"""
+    os.unlink(f)
+    # try removing directories that might now be empty
+    try:
+        os.removedirs(os.path.dirname(f))
+    except OSError:
+        pass
+

mercurial/util.py

@@ -390,15 +390,6 b' def checksignature(func):'
 
     return check
 
-def unlinkpath(f):
-    """unlink and remove the directory if it is empty"""
-    os.unlink(f)
-    # try removing directories that might now be empty
-    try:
-        os.removedirs(os.path.dirname(f))
-    except OSError:
-        pass
-
 def copyfile(src, dest):
     "copy a file, preserving mode and atime/mtime"
     if os.path.islink(src):