manifest: remove optional default= argument on flags(path)

manifest: remove optional default= argument on flags(path)

It had only one caller inside manifest.py, and treemanifest was
actually incorrectly implemented. treemanifest is still missing the
fastdelta() method from the interface (and so doesn't yet conform),
but this is at least progress.

Differential Revision: https://phab.mercurial-scm.org/D8069

--- a/mercurial/interfaces/repository.py	Mon Feb 03 11:56:02 2020 -0500
+++ b/mercurial/interfaces/repository.py	Mon Feb 03 22:16:36 2020 -0500
@@ -1027,8 +1027,8 @@
     def get(path, default=None):
         """Obtain the node value for a path or a default value if missing."""
 
-    def flags(path, default=b''):
-        """Return the flags value for a path or a default value if missing."""
+    def flags(path):
+        """Return the flags value for a path (default: empty bytestring)."""
 
     def copy():
         """Return a copy of this manifest."""

--- a/mercurial/manifest.py	Mon Feb 03 11:56:02 2020 -0500
+++ b/mercurial/manifest.py	Mon Feb 03 22:16:36 2020 -0500
@@ -460,7 +460,7 @@
     __bool__ = __nonzero__
 
     def __setitem__(self, key, node):
-        self._lm[key] = node, self.flags(key, b'')
+        self._lm[key] = node, self.flags(key)
 
     def __contains__(self, key):
         if key is None:
@@ -595,11 +595,11 @@
         except KeyError:
             return default
 
-    def flags(self, key, default=b''):
+    def flags(self, key):
         try:
             return self._lm[key][1]
         except KeyError:
-            return default
+            return b''
 
     def copy(self):
         c = manifestdict()