Problem: Syntax test fails when run with non C locale
Solution: Run syntax tests with C locale, clean up Xtestscript file,
strip environment variables from GetVimCommand()
(h-east)
closes: #14007
Co-authored-by: h-east <h.east.727@gmail.com>
Signed-off-by: h-east <h.east.727@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>