test(oldtest): unskip existing tests that use Blobs

src/nvim/testdir/test_rename.vim

@@ -95,7 +95,6 @@ func Test_rename_copy()
 endfunc
 
 func Test_rename_fails()
-  throw 'skipped: TODO: '
   call writefile(['foo'], 'Xrenamefile')
 
   " Can't rename into a non-existing directory.

src/nvim/testdir/test_swap.vim

@@ -168,7 +168,6 @@ func Test_swapname()
 endfunc
 
 func Test_swapfile_delete()
-  throw 'skipped: need the "blob" feature for this test'
   autocmd! SwapExists
   function s:swap_exists()
     let v:swapchoice = s:swap_choice

src/nvim/testdir/test_undo.vim

@@ -368,7 +368,6 @@ endfunc
 
 " Check that reading a truncted undo file doesn't hang.
 func Test_undofile_truncated()
-  throw 'skipped: TODO: '
   new
   call setline(1, 'hello')
   set ul=100