merge(third_party/git): Merge squashed git subtree at v2.23.0

Merge commit '1b593e1ea4' as 'third_party/git'

third_party/git/Documentation/git-prune-packed.txt

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+git-prune-packed(1)
+===================
+
+NAME
+----
+git-prune-packed - Remove extra objects that are already in pack files
+
+
+SYNOPSIS
+--------
+[verse]
+'git prune-packed' [-n|--dry-run] [-q|--quiet]
+
+
+DESCRIPTION
+-----------
+This program searches the `$GIT_OBJECT_DIRECTORY` for all objects that currently
+exist in a pack file as well as the independent object directories.
+
+All such extra objects are removed.
+
+A pack is a collection of objects, individually compressed, with delta
+compression applied, stored in a single file, with an associated index file.
+
+Packs are used to reduce the load on mirror systems, backup engines,
+disk storage, etc.
+
+
+OPTIONS
+-------
+-n::
+--dry-run::
+        Don't actually remove any objects, only show those that would have been
+        removed.
+
+-q::
+--quiet::
+	Squelch the progress indicator.
+
+SEE ALSO
+--------
+linkgit:git-pack-objects[1]
+linkgit:git-repack[1]
+
+GIT
+---
+Part of the linkgit:git[1] suite