Revert "use list of funcrecs, allowing window overrides to be dynamically added"

This reverts commit c0427e435d.

autoload/airline.vim

@@ -68,9 +68,7 @@ function! s:apply_window_overrides()
     let w:airline_section_c = bufname(winbufnr(winnr()))
   endif
 
-  for FuncRef in g:airline_window_override_funcrefs
+  call airline#extensions#apply_window_overrides()
-    call FuncRef()
-  endfor
 endfunction
 
 function! airline#update_externals()

autoload/airline/extensions.vim

@@ -10,8 +10,12 @@ function! airline#extensions#load()
           \ 'prog': 'airline#extensions#ctrlp#ctrlp_airline_status',
           \ }
   endif
+endfunction
 
-  call add(g:airline_window_override_funcrefs, function('s:apply_window_overrides'))
+function! s:empty_sections()
+  for section in s:sections
+    let w:airline_section_{section} = ''
+  endfor
 endfunction
 
 function! s:override_left_only(section1, section2)
@@ -21,7 +25,7 @@ function! s:override_left_only(section1, section2)
   let w:airline_left_only = 1
 endfunction
 
-function! s:apply_window_overrides()
+function! airline#extensions#apply_window_overrides()
   silent! unlet w:airline_left_only
   for section in s:sections
     silent! unlet w:airline_section_{section}

plugin/airline.vim

@@ -50,8 +50,6 @@ function! s:init()
   endif
 endfunction
 
-let g:airline_window_override_funcrefs = []
-
 augroup airline
   au!
   autocmd ColorScheme * call airline#highlight(['normal'])