largefiles: drop unnecessary setting of matcher._always

In two very similar segments of code, an existing matcher is modified
by changing its _files attribute through a map and a filter
operation. Neither operation can cause an empty list to become
non-empty, so a matcher that always matches can not stop always
matching. Drop the setting of the attribute, so we don't unnecessarily
prevent the fast paths to be taken where these matchers end up being
used.

hgext/largefiles/overrides.py

@@ -576,7 +576,6 b' def overridecopy(orig, ui, repo, pats, o'
                 lfile = lambda f: lfutil.standin(f) in manifest
                 m._files = [lfutil.standin(f) for f in m._files if lfile(f)]
                 m._fmap = set(m._files)
-                m._always = False
                 origmatchfn = m.matchfn
                 m.matchfn = lambda f: (lfutil.isstandin(f) and
                                     (f in manifest) and
@@ -684,7 +683,6 b' def overriderevert(orig, ui, repo, *pats'
             m._files = [tostandin(f) for f in m._files]
             m._files = [f for f in m._files if f is not None]
             m._fmap = set(m._files)
-            m._always = False
             origmatchfn = m.matchfn
             def matchfn(f):
                 if lfutil.isstandin(f):