tags: remove scary message about corrupt tags cache

Caches should be transparent. If a cache is damaged, it should
silently be rebuilt, much like if it were invalid. No one seems to
have ever hit this in the wild.

mercurial/tags.py

@@ -272,7 +272,6 b' def _readtagcache(ui, repo):'
                     cachefnode[headnode] = fnode
         except Exception:
             # corruption of the tags cache, just recompute it
-            ui.warn(_('.hg/cache/tags is corrupt, rebuilding it\n'))
             cacheheads = []
             cacherevs = []
             cachefnode = {}

tests/test-tags.t

@@ -38,7 +38,6 b' Try corrupting the cache'
 
   $ printf 'a b' > .hg/cache/tags
   $ hg identify
-  .hg/cache/tags is corrupt, rebuilding it
   acb14030fe0a tip
   $ cacheexists
   tag cache exists