vfs: drop the 'mustaudit' API

vfs: drop the 'mustaudit' API

There are no remaining users of 'mustaudit' so we can safely drop the API.
External user are unlikely from a quick research so no deprecation is added.

--- a/mercurial/vfs.py	Sun Jul 02 04:26:34 2017 +0200
+++ b/mercurial/vfs.py	Sun Jul 02 04:26:42 2017 +0200
@@ -290,21 +290,13 @@
         if realpath:
             base = os.path.realpath(base)
         self.base = base
-        self.mustaudit = audit
-        self.createmode = None
-        self._trustnlink = None
-
-    @property
-    def mustaudit(self):
-        return self._audit
-
-    @mustaudit.setter
-    def mustaudit(self, onoff):
-        self._audit = onoff
-        if onoff:
+        self._audit = audit
+        if audit:
             self.audit = pathutil.pathauditor(self.base)
         else:
             self.audit = util.always
+        self.createmode = None
+        self._trustnlink = None
 
     @util.propertycache
     def _cansymlink(self):
@@ -436,14 +428,6 @@
         self.vfs = vfs
 
     @property
-    def mustaudit(self):
-        return self.vfs.mustaudit
-
-    @mustaudit.setter
-    def mustaudit(self, onoff):
-        self.vfs.mustaudit = onoff
-
-    @property
     def options(self):
         return self.vfs.options