options: Remove 'esckeys' (#6138)

This was never supported and it does not make sense for Nvim.

src/nvim/options.lua

@@ -710,13 +710,6 @@ return {
       varname='p_efm',
       defaults={if_true={vi=macros('DFLT_EFM')}}
     },
-    {
-      full_name='esckeys', abbreviation='ek',
-      type='bool', scope={'global'},
-      vim=true,
-      varname='p_ek',
-      defaults={if_true={vi=false, vim=true}}
-    },
     {
       full_name='eventignore', abbreviation='ei',
       type='string', list='onecomma', scope={'global'},