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/muttrc.vim b/runtime/ftplugin/muttrc.vim
index c9f6df3..7df6158 100644
--- a/runtime/ftplugin/muttrc.vim
+++ b/runtime/ftplugin/muttrc.vim
@@ -1,7 +1,7 @@
 " Vim filetype plugin file
 " Language:             mutt RC File
 " Previous Maintainer:  Nikolai Weibull <now@bitwi.se>
-" Latest Revision:      2023-10-07
+" Latest Revision:      2024-09-19 (simplify keywordprg #15696)
 
 if exists("b:did_ftplugin")
   finish
@@ -18,20 +18,12 @@
 
 let &l:include = '^\s*source\>'
 
-if has('unix') && executable('less')
-  if !has('gui_running')
-    command -buffer -nargs=1 MuttrcKeywordPrg
-          \ silent exe '!' . 'LESS= MANPAGER="less --pattern=''^\s+' . <q-args> . '\b'' --hilite-search" man ' . 'muttrc' |
-          \ redraw!
-  elseif has('terminal')
-    command -buffer -nargs=1 MuttrcKeywordPrg
-          \ silent exe 'term ' . 'env LESS= MANPAGER="less --pattern=''' . escape('^\s+' . <q-args> . '\b', '\') . ''' --hilite-search" man ' . 'muttrc'
-  endif
-  if exists(':MuttrcKeywordPrg') == 2
-    setlocal iskeyword+=-
-    setlocal keywordprg=:MuttrcKeywordPrg
-    let b:undo_ftplugin .= '| setlocal keywordprg< iskeyword< | sil! delc -buffer MuttrcKeywordPrg'
-  endif
+if has('unix') && executable('less') && exists(':terminal') == 2
+  command -buffer -nargs=1 MuttrcKeywordPrg
+        \ silent exe 'term ' . 'env LESS= MANPAGER="less --pattern=''' . escape('^\s+' . <q-args> . '\b', '\') . ''' --hilite-search" man ' . 'muttrc'
+  setlocal iskeyword+=-
+  setlocal keywordprg=:MuttrcKeywordPrg
+  let b:undo_ftplugin .= '| setlocal keywordprg< iskeyword< | sil! delc -buffer MuttrcKeywordPrg'
 endif
 
 let &cpo = s:cpo_save