Improve ExplainState type handling in header files

Now that we can have repeat typedefs with C11, we don't need to use
"struct ExplainState" anymore but can instead make a typedef where
necessary.  This doesn't change anything but makes it look nicer.

(There are more opportunities for similar changes, but this is broken
out because there was a separate discussion about it, and it's
somewhat bulky on its own.)

Reviewed-by: Chao Li <li.evan.chao@gmail.com>
Discussion: https://www.postgresql.org/message-id/flat/f36c0a45-98cd-40b2-a7cc-f2bf02b12890%40eisentraut.org#a12fb1a2c1089d6d03010f6268871b00
Discussion: https://www.postgresql.org/message-id/flat/10d32190-f31b-40a5-b177-11db55597355@eisentraut.org

0 files changed, 0 insertions, 0 deletions