runtime(groff,nroff): improve ftplugin

- set options in ftplugin but not in syntax
- implement ftplugin/groff.vim (wrapper of ftplugin/nroff.vim)

closes: #17174

Signed-off-by: Eisuke Kawashima <e-kwsm@users.noreply.github.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/runtime/syntax/nroff.vim b/runtime/syntax/nroff.vim
index 5667042..fec966f 100644
--- a/runtime/syntax/nroff.vim
+++ b/runtime/syntax/nroff.vim
@@ -4,6 +4,7 @@
 " Previous Maintainer:	Pedro Alejandro López-Valencia <palopezv@gmail.com>
 " Previous Maintainer:	Jérôme Plût <Jerome.Plut@ens.fr>
 " Last Change:	2021 Mar 28
+"	2025 Apr 24 by Eisuke Kawashima (move options from syntax to ftplugin #17174)
 "
 " {{{1 Todo
 "
@@ -40,19 +41,6 @@
 	syn match nroffError /\s\+$/
 	syn match nroffSpaceError /[.,:;!?]\s\{2,}/
 endif
-"
-"
-" {{{1 Special file settings
-"
-" {{{2  ms exdented paragraphs are not in the default paragraphs list.
-"
-setlocal paragraphs+=XP
-"
-" {{{2 Activate navigation to preprocessor sections.
-"
-if exists("b:preprocs_as_sections")
-	setlocal sections=EQTSPS[\ G1GS
-endif
 
 " {{{1 Escape sequences
 " ------------------------------------------------------------