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/readline.vim b/runtime/ftplugin/readline.vim
index f5934ce..77fab2a 100644
--- a/runtime/ftplugin/readline.vim
+++ b/runtime/ftplugin/readline.vim
@@ -2,7 +2,7 @@
 " Language:		readline(3) configuration file
 " Maintainer:		Doug Kearns <dougkearns@gmail.com>
 " Previous Maintainer:	Nikolai Weibull <now@bitwi.se>
-" Last Change:		2023 Aug 22
+" Last Change:		2024 Sep 19 (simplify keywordprg #15696)
 
 if exists("b:did_ftplugin")
   finish
@@ -34,20 +34,12 @@
   let b:undo_ftplugin ..= " | unlet! b:browsefilter"
 endif
 
-if has('unix') && executable('less')
-  if !has('gui_running')
-    command -buffer -nargs=1 ReadlineKeywordPrg
-          \ silent exe '!' . 'LESS= MANPAGER="less --pattern=''^\s+' . <q-args> . '\b'' --hilite-search" man ' . '3 readline' |
-          \ redraw!
-  elseif has('terminal')
-    command -buffer -nargs=1 ReadlineKeywordPrg
-          \ silent exe 'term ' . 'env LESS= MANPAGER="less --pattern=''' . escape('^\s+' . <q-args> . '\b', '\') . ''' --hilite-search" man ' . '3 readline'
-  endif
-  if exists(':ReadlineKeywordPrg') == 2
-    setlocal iskeyword+=-
-    setlocal keywordprg=:ReadlineKeywordPrg
-    let b:undo_ftplugin .= '| setlocal keywordprg< iskeyword< | sil! delc -buffer ReadlineKeywordPrg'
-  endif
+if has('unix') && executable('less') && exists(':terminal') == 2
+  command -buffer -nargs=1 ReadlineKeywordPrg
+        \ silent exe 'term ' . 'env LESS= MANPAGER="less --pattern=''' . escape('^\s+' . <q-args> . '\b', '\') . ''' --hilite-search" man ' . '3 readline'
+  setlocal iskeyword+=-
+  setlocal keywordprg=:ReadlineKeywordPrg
+  let b:undo_ftplugin .= '| setlocal keywordprg< iskeyword< | sil! delc -buffer ReadlineKeywordPrg'
 endif
 
 let &cpo = s:cpo_save