test: hoist buf_lines()

test/functional/plugin/lsp_spec.lua

@@ -729,10 +729,6 @@ describe('LSP util', function()
     }
   end
 
-  local function buf_lines(bufnr)
-    return exec_lua("return vim.api.nvim_buf_get_lines((...), 0, -1, false)", bufnr)
-  end
-
   describe('apply_edits', function()
     it('should apply simple edits', function()
       local edits = {