check.vim: Use silent command modifier

check.vim: Use silent command modifier

Problem:  When checking a .po file (make -C src/po check), errors are not
          displayed.

Solution: Adding "silent" to some normal commands in check.vim
          suppresses unnecessary output (Muraoka Taro)

This is because the output of check.vim is redirected to /dev/null.
However, if you stop the redirection, check.vim generates a lot of
output and becomes very slow.

When these commands are run in ex mode, they output the contents of the
line the cursor is pointing to.  This caused a lot of output.

closes: #19227

Signed-off-by: Muraoka Taro <koron.kaoriya@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>