Update templates/system.txt

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: mingcheng

templates/system.txt

@@ -37,7 +37,6 @@ Please generate a git commit message with the specified requirements.
 
 - Capitalize first letter in the header
 - No trailing period in the header
-- No period in header
 - Blank line between header and body
 - Body uses bullet points
 - No Capitalize in the body