Remove unused methods

Manila doesn't use methods ensure_tree and delete_if_exists anywhere,
and oslo.utils provides same methods in module fileutils. We can use
them from oslo.utils if we need in the futrue.

TrivialFix

Change-Id: I280b674dca3738d26c2bed2cf71e94775b370cd5

manila/utils.py

@@ -219,18 +219,6 @@ class LazyPluggable(object):
         return getattr(backend, key)
 
 
-def delete_if_exists(pathname):
-    """Delete a file, but ignore file not found error."""
-
-    try:
-        os.unlink(pathname)
-    except OSError as e:
-        if e.errno == errno.ENOENT:
-            return
-        else:
-            raise
-
-
 def get_from_path(items, path):
     """Returns a list of items matching the specified path.
 
@@ -476,21 +464,6 @@ def walk_class_hierarchy(clazz, encountered=None):
             yield subclass
 
 
-def ensure_tree(path):
-    """Create a directory (and any ancestor directories required)
-
-    :param path: Directory to create
-    """
-    try:
-        os.makedirs(path)
-    except OSError as exc:
-        if exc.errno == errno.EEXIST:
-            if not os.path.isdir(path):
-                raise
-        else:
-            raise
-
-
 def cidr_to_netmask(cidr):
     """Convert cidr to netmask."""
     try: