Print planning time only in EXPLAIN ANALYZE, not plain EXPLAIN.

We've gotten enough push-back on that change to make it clear that it
wasn't an especially good idea to do it like that.  Revert plain EXPLAIN
to its previous behavior, but keep the extra output in EXPLAIN ANALYZE.
Per discussion.

Internally, I set this up as a separate flag ExplainState.summary that
controls printing of planning time and execution time.  For now it's
just copied from the ANALYZE option, but we could consider exposing it
to users.

src/include/commands/explain.h

@@ -30,9 +30,10 @@ typedef struct ExplainState
 	/* options */
 	bool		verbose;		/* be verbose */
 	bool		analyze;		/* print actual times */
-	bool		costs;			/* print costs */
+	bool		costs;			/* print estimated costs */
 	bool		buffers;		/* print buffer usage */
-	bool		timing;			/* print timing */
+	bool		timing;			/* print detailed node timing */
+	bool		summary;		/* print total planning and execution timing */
 	ExplainFormat format;		/* output format */
 	/* other states */
 	PlannedStmt *pstmt;			/* top of plan */