Revert changes to restore cursor position after undo

This feature is nice and desirable, but it was implemented in a intrusive way
by modifying the sequence of bytes we emit when running a command; this in
turn requires changing a bunch of tests.

This sequence hasn't changed in decades and the consequences of changing it
are hard to predict, given that it is likely terminal dependent; we've
already found a regression.

It's fine to reintroduce this but it should be done in a less intrusive way
(conceptually that seems straightforward - we're just remembering the cursor
position).

Revert "Fix spurious blank lines when executing scrolled commandline"

This reverts commit 0e512f8033.

Revert "On undo after execute, restore the cursor position "

This reverts commit 610338cc70.

tests/pexpects/read.py

@@ -1,5 +1,5 @@
 #!/usr/bin/env python3
-from pexpect_helper import SpawnedProc, TO_END
+from pexpect_helper import SpawnedProc
 
 sp = SpawnedProc()
 send, sendline, sleep, expect_prompt, expect_re, expect_str = (
@@ -17,7 +17,7 @@ def expect_read_prompt():
 
 
 def expect_marker(text):
-    expect_prompt(TO_END + "@MARKER:" + str(text) + "@\\r\\n")
+    expect_prompt("\r\n.*@MARKER:" + str(text) + "@\\r\\n")
 
 
 def print_var_contents(varname, expected):