makeqstrdefs: don't make _and_, _or_ poisoned substrings for QSTRs

New contributor @mdroberts1243 encountered an interesting problem in
which the argument they had named "column_underscore_and_page_addressing"
simply couldn't be used; I discovered that internally this had been
transformed into "column_underscore∧page_addressing", because QSTR
makes _ENTITY_ stand for the same thing as &ENTITY; does in HTML.

This might be nice for some things, but we don't want it here!
I was unable to find a sensible way to "escape" and prevent this entity
coding, so instead I ripped out support for the _and_ and _or_ escapes.

py/makeqstrdefs.py

@@ -57,6 +57,10 @@ name2codepoint['caret'] = ord('^')
 name2codepoint['pipe'] = ord('|')
 name2codepoint['tilde'] = ord('~')
 
+# These are just vexing!
+del name2codepoint['and']
+del name2codepoint['or']
+
 def write_out(fname, output):
     if output:
         for m, r in [("/", "__"), ("\\", "__"), (":", "@"), ("..", "@@")]: