feat(ex_cmds)!: remove :behave

just use the individual options instead.

   set selection=exclusive
   set selectmode=mouse,key
   set mousemodel=popup
   set keymodel=startsel,stopsel

src/nvim/ex_cmds.lua

@@ -196,12 +196,6 @@ module.cmds = {
     addr_type='ADDR_BUFFERS',
     func='ex_bunload',
   },
-  {
-    command='behave',
-    flags=bit.bor(BANG, NEEDARG, WORD1, TRLBAR, CMDWIN, LOCK_OK),
-    addr_type='ADDR_NONE',
-    func='ex_behave',
-  },
   {
     command='belowright',
     flags=bit.bor(NEEDARG, EXTRA, NOTRLCOM),