Vim: remove Syntastic plugin

I'd like to try out Ale, a Vim plugin for syntax checking that works
asynchronously. It has been a good run with Syntastic, and perhaps I'll
return some day once it gets async support.

vim-syntastic/syntastic#699

.gitmodules

@@ -38,9 +38,6 @@
 [submodule ".vim/bundle/vim-multiple-cursors"]
 	path = .vim/bundle/vim-multiple-cursors
 	url = https://github.com/terryma/vim-multiple-cursors.git
-[submodule ".vim/bundle/syntastic"]
-	path = .vim/bundle/syntastic
-	url = https://github.com/scrooloose/syntastic.git
 [submodule ".vim/bundle/vim-vinegar"]
 	path = .vim/bundle/vim-vinegar
 	url = https://github.com/tpope/vim-vinegar.git

.vim/plugin/statusline.vim

@@ -21,11 +21,6 @@ if has('statusline')
 
   set statusline+=%= " split point for left and right groups
 
-  set statusline+=%#Error# " switch to Error highlight group
-  set statusline+=%{SyntasticStatuslineFlag()} " configured by syntastic_stl_format
-  set statusline+=%* " reset highlight group
-
-  set statusline+=\  " space
   set statusline+=%{statusline#file_size()} " File size
   set statusline+=\  " space
   set statusline+=%1* " switch to User1 highlight group (italics)