vitalizer: Liberate from 'redir'

'redir' cannnot be nested and cannot be used in execute() function.

The main reason why vital.vim used 'redir' has solved on Vim 8.0.1425 and vital.vim
now supports Vim 8.1 or later thus we can use execute() instead.

Author: lambdalisue

autoload/vital/vital.vim

@@ -186,12 +186,7 @@ function! s:_format_throwpoint(throwpoint) abort
 endfunction
 
 function! s:_get_file_by_func_name(name) abort
-  try
-    redir => body
-    silent execute 'verbose function' a:name
-  finally
-    redir END
-  endtry
+  let body = execute(printf('verbose function %s', a:name))
   let lines = split(body, "\n")
   let signature = matchstr(lines[0], '^\s*\zs.*')
   let file = matchstr(lines[1], '^\t\%(Last set from\|.\{-}:\)\s*\zs.*$')
@@ -265,7 +260,7 @@ function! s:_sid(path, filter_pattern) abort
   if has_key(s:cache_sid, unified_path)
     return s:cache_sid[unified_path]
   endif
-  for line in filter(split(s:_execute(':scriptnames'), "\n"), 'v:val =~# a:filter_pattern')
+  for line in filter(split(execute(':scriptnames'), "\n"), 'v:val =~# a:filter_pattern')
     let [_, sid, path; __] = matchlist(line, '^\s*\(\d\+\):\s\+\(.\+\)\s*$')
     if s:_unify_path(path) is# unified_path
       let s:cache_sid[unified_path] = sid
@@ -275,21 +270,6 @@ function! s:_sid(path, filter_pattern) abort
   return 0
 endfunction
 
-" We want to use an execute() builtin function instead of s:_execute(),
-" however there is a bug in execute().
-" execute() returns empty string when it is called in
-" completion function of user defined ex command.
-" https://github.com/vim-jp/issues/issues/1129
-function! s:_execute(cmd) abort
-  let [save_verbose, save_verbosefile] = [&verbose, &verbosefile]
-  set verbose=0 verbosefile=
-  redir => res
-    silent! execute a:cmd
-  redir END
-  let [&verbose, &verbosefile] = [save_verbose, save_verbosefile]
-  return res
-endfunction
-
 if filereadable(expand('<sfile>:r') . '.VIM') " is case-insensitive or not
   let s:_unify_path_cache = {}
   " resolve() is slow, so we cache results.
@@ -314,7 +294,7 @@ endif
 " copied and modified from Vim.ScriptLocal
 let s:SNR = join(map(range(len("\<SNR>")), '"[\\x" . printf("%0x", char2nr("\<SNR>"[v:val])) . "]"'), '')
 function! s:sid2sfuncs(sid) abort
-  let fs = split(s:_execute(printf(':function /^%s%s_', s:SNR, a:sid)), "\n")
+  let fs = split(execute(printf(':function /^%s%s_', s:SNR, a:sid)), "\n")
   let r = {}
   let pattern = printf('\m^function\s<SNR>%d_\zs\w\{-}\ze(', a:sid)
   for fname in map(fs, 'matchstr(v:val, pattern)')