Remove duplicate definition of TransactionId.

Remove duplicate definition of TransactionId.

Since commit: ca300f839, following is defined in
src/include/parser/pg_list.h and src/include/parser/primnodes.h.

typedef uint32 TransactionId;

This is harmless in moder OS/compilers, but an old RHEL5 user reported
that this results in compile error:
https://www.pgpool.net/pipermail/pgpool-general/2023-December/009040.html

So remove the definition from primnodes.h (remove it from pg_list.h
causes another compile error).

Back patched to V4_5_STABLE.