[L10N] Kickoff for Git 2.21.0 round #2

Hi,

Git v2.21.0-rc1 introduced 3 update messages from commit 32ceace39f (Fix typos in translatable strings for v2.21.0, 2019-02-11). let's start new round of git l10n based on the following commit:

    l10n: git.pot: v2.21.0 round 2 (3 new, 3 removed)
    
    Introduce 3 update messages for v2.21.0 l10n round 2 from commit
    32ceace39f (Fix typos in translatable strings for v2.21.0, 2019-02-11).
    
    Signed-off-by: Jiang Xin <worldhello.net@gmail.com>

You can get it from the usual place:

    https://github.com/git-l10n/git-po/

As how to update your XX.po and help to translate Git, please see "Updating a XX.po file" and other sections in "po/README" file.

-- Jiang Xin