'cpoptions': Remove "*" flag #2554

The "*" flag in 'cpoptions' makes the command :* execute the contents of
a register. Removed because
  1. the same functionality exists as :@
  2. it hides :* as a useful command-line shortcut for :'<,'>
  3. unlike :@ it cannot be used with the * register

Helped-by: Michael Reed <m.reed@mykolab.com>

src/nvim/ex_cmds.lua

@@ -3136,13 +3136,6 @@ return {
     addr_type=ADDR_LINES,
     func='do_sub',
   },
-  {
-    command='*',
-    enum='CMD_star',
-    flags=bit.bor(RANGE, WHOLEFOLD, EXTRA, TRLBAR, CMDWIN),
-    addr_type=ADDR_LINES,
-    func='ex_at',
-  },
   {
     command='<',
     enum='CMD_lshift',