runtime(misc): simplify keywordprg in various ftplugins

closes: #15696

Signed-off-by: Konfekt <Konfekt@users.noreply.github.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/runtime/ftplugin/zsh.vim b/runtime/ftplugin/zsh.vim
index 5e69336..5d4f4fe 100644
--- a/runtime/ftplugin/zsh.vim
+++ b/runtime/ftplugin/zsh.vim
@@ -19,9 +19,7 @@
 let b:undo_ftplugin = "setl com< cms< fo< "
 
 if executable('zsh') && &shell !~# '/\%(nologin\|false\)$'
-  if !has('gui_running') && executable('less')
-    command! -buffer -nargs=1 ZshKeywordPrg silent exe '!MANPAGER= zsh -c "autoload -Uz run-help; run-help <args> 2>/dev/null | LESS= less"' | redraw!
-  elseif has('terminal')
+  if exists(':terminal') == 2
     command! -buffer -nargs=1 ZshKeywordPrg silent exe ':term zsh -c "autoload -Uz run-help; run-help <args>"'
   else
     command! -buffer -nargs=1 ZshKeywordPrg echo system('MANPAGER= zsh -c "autoload -Uz run-help; run-help <args> 2>/dev/null"')