clipboard: Revert unused check neovim#9309

PR neovim#9304 added support for functions in clipboard providers. As part of
the PR I meant to move two checks in the provider code out of an if
statement into separate statements and adding additional checks for
g:clipboard attributes - as it turns out the code is wrong and it does
not implement additional checks while it adds two conditions that make
very little sense

    type(g:clipboard['copy']) #isnot# v:t_func

what would make sense would be something along the lines of

    type(g:clipboard['copy']['+']) #isnot# v:t_func

but might not be what we want either, so I'm reverting this.

runtime/autoload/provider/clipboard.vim

@@ -55,22 +55,12 @@ endfunction
 function! provider#clipboard#Executable() abort
   if exists('g:clipboard')
     if type({}) isnot# type(g:clipboard)
+          \ || type({}) isnot# type(get(g:clipboard, 'copy', v:null))
+          \ || type({}) isnot# type(get(g:clipboard, 'paste', v:null))
       let s:err = 'clipboard: invalid g:clipboard'
       return ''
     endif
 
-    if type(get(g:clipboard, 'copy', v:null)) isnot# v:t_dict
-        \ && type(get(g:clipboard, 'copy', v:null)) isnot# v:t_func
-      let s:err = "clipboard: invalid g:clipboard['copy']"
-      return ''
-    endif
-
-    if type(get(g:clipboard, 'paste', v:null)) isnot# v:t_dict
-        \ && type(get(g:clipboard, 'paste', v:null)) isnot# v:t_func
-      let s:err = "clipboard: invalid g:clipboard['paste']"
-      return ''
-    endif
-
     let s:copy = get(g:clipboard, 'copy', { '+': v:null, '*': v:null })
     let s:paste = get(g:clipboard, 'paste', { '+': v:null, '*': v:null })
     let s:cache_enabled = get(g:clipboard, 'cache_enabled', 0)