l10n: vi.po (2210t): Updated git-core translation

 * Updated new strings
 * Fix typos and review
 * Change meaning of stage

Signed-off-by: Tran Ngoc Quan <vnwildman@gmail.com>
l10n: zh_CN.po: translate 27 messages (2210t0f0u)

Translate 27 new messages came from git.pot update in v1.9-rc0-1-gdf49095
(l10n: git.pot: v1.9 round 1 (27 new, 11 removed)). Also update
translatons on "graft" and "reference repository".

Signed-off-by: Jiang Xin <worldhello.net@gmail.com>
l10n: remove 2 blank translations on Danish, Dutch

Two l10n teams haven't contributed a single translation for about two
years since they was initialized with a blank template.  Remove them
can make the Git package smaller and give opportunities to other
contributors.

Signed-off-by: Jiang Xin <worldhello.net@gmail.com>