runtime(vim): update Vim Syntax generator

- Add missing "Last Change:" line.
- The date on this line in vim.vim is updated by update_date.vim at
  Make time. (I made a mistake in the file path)
- Remove unnecessary "b:loaded_syntax_vim_ex".
- Remove "Base File Date:" line in vim.vim.base
- Add Doug Kearns as Maintainer

closes: #14031

Signed-off-by: h-east <h.east.727@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

runtime/syntax/generator/Makefile

@@ -16,7 +16,6 @@ vim.vim: vim.vim.rc update_date.vim
 	@echo "Generating vim.vim ..."
 	@cp -f vim.vim.rc ../vim.vim
 	@$(RUN_VIM) -S update_date.vim
-	@sed -i -e 's/__REVISION__/$(REVISION)/' ../vim.vim
 	@echo "done."
 
 vim.vim.rc: gen_syntax_vim.vim vim.vim.base $(SRC)