manifestcache: actually honor --clear

Before this change, the --clear flag was not clearing the on disk cache.
(We also remove the extra verbosity when using --clear. Same as what we did for --add)

mercurial/debugcommands.py

@@ -1478,7 +1478,8 b' def debugmanifestfulltextcache(ui, repo,'
     if opts.get(r'clear'):
         with repo.lock():
             cache = getcache()
-            cache.clear()
+            cache.clear(clear_persisted_data=True)
+            return
 
     if add:
         with repo.lock():

tests/test-manifest.t

@@ -142,3 +142,9 b' Accessing the initial entry again, refre'
   id: 1e01206b1d2f72bd55f2a33fa8ccad74144825b7, size 133 bytes
   id: fce2a30dedad1eef4da95ca1dc0004157aa527cf, size 87 bytes
   total cache data size 268 bytes, on-disk 268 bytes
+
+Check cache clearing
+
+  $ hg debugmanifestfulltextcache --clear
+  $ hg debugmanifestfulltextcache
+  cache empty