vim-patch:8.1.1585: :let-heredoc does not trim enough

Problem:    :let-heredoc does not trim enough.
Solution:   Trim indent from the contents based on the indent of the first
            line.  Use let-heredoc in more tests.
e7eb92708e

This is a missing part of Vim patch 8.1.1585 from #11211.

src/nvim/testdir/test_cindent.vim

@@ -3243,32 +3243,32 @@ func Test_cindent_30()
   setl cindent ts=4 sw=4
   setl cino=+20
 
-  let code =<< trim [CODE]
+  let code =<< [CODE]
 	void
-  foo()
-  {
+foo()
+{
 	if (a)
 	{
 	} else
 		asdf;
-  }
-  [CODE]
+}
+[CODE]
 
   call append(0, code)
   normal gg
   normal ]]=][
 
-  let expected =<< trim [CODE]
+  let expected =<< [CODE]
 	void
-  foo()
-  {
+foo()
+{
 	if (a)
 	{
 	} else
 		asdf;
-  }
+}
 
-  [CODE]
+[CODE]
 
   call assert_equal(expected, getline(1, '$'))
   enew! | close