Make upgradecheck a no-op in MSVC's vcregress.pl

322becb has changed upgradecheck to use the TAP tests, discarding
pg_upgrade's tests in bincheck.  However, this is proving to be a bad
idea for the Windows buildfarm clients that use MSVC when TAP tests are
disabled as this causes a hard failure at the pg_upgrade step.

This commit disables upgradecheck, moving the execution of the tests of
pg_upgrade to bincheck, as per an initial suggestion from Andres
Freund, so as the buildfarm is able to live happily with those changes.

While on it, remove the routine that was used by upgradecheck to
create databases whose names are generated with a range of ASCII
characters as it is not used since 322becb.  upgradecheck is removed
from the CI script for Windows, as bincheck takes care of that now.

Per report from buildfarm member hamerkop (MSVC 2017 without a TAP
setup).

Reviewed-by: Justin Pryzby
Discussion: https://postgr.es/m/YkbnpriYEAagZ2wH@paquier.xyz

doc/src/sgml/install-windows.sgml

@@ -470,7 +470,6 @@ $ENV{CONFIG}="Debug";
 <userinput>vcregress isolationcheck</userinput>
 <userinput>vcregress bincheck</userinput>
 <userinput>vcregress recoverycheck</userinput>
-<userinput>vcregress upgradecheck</userinput>
 </screen>
 
    To change the schedule used (default is parallel), append it to the