Make 'tis620-2533' character set be an alias for 'thai-iso8859-11'

Make 'tis620-2533' character set be an alias for 'thai-iso8859-11'

* lisp/simple.el (what-cursor-position): Revert ad-hoc change
to work around tis620-2533 charset.
* lisp/w32-fns.el: Use thai-iso8859-11 instead of tis620-2533.
* lisp/international/mule-conf.el (tis620-2533): Now an alias
for thai-iso8859-11, not a separate character set.
* lisp/international/fontset.el (charset-script-alist): Add
thai-iso8859-11; fix entries for greek and hebrew.
(font-encoding-alist, font-encoding-charset-alist): Use
thai-iso8859-11 instead of tis620-2533.
* lisp/descr-text.el (describe-char): Remove the ad-hoc code
that assigns eight-bit-control characters to the eight-bit
charset.