Lift compile time default maximum pattern length about pcre2

[PhilipHazel]

I am not at all keen on making such a change, for a number of reasons:

1. It's a serious incompatible change that may affect existing users. I don't like doing that.
2. There are very many PCRE2 users for whom 64K is more than enough. I'm thinking of, for example, email routing (for which I originally wrote PCRE), text editing, and similar applications where the patterns are generally quite short.
3. I know (because there have been issues in the past) that there are applications using PCRE2 that run very large numbers of separate threads, each of which has very limited memory. Such a change may well impact them.
4. There is of course a performance cost, though it would depend very much on the pattern details.

If I were starting again (knowing what I now know) I would certainly do things differently, probably always compiling into 32-bit units, but hindsight is always 20/20.