pg_upgrade: Fix some minor code issues

96ef3b8f accidentally copied a not
applicable comment from the float8_pass_by_value code to the
data_checksums code.  Remove that.

87d3b35a changed pg_upgrade to
checking the checksum version rather than just the Boolean presence of
checksums, but didn't change the field type in its ControlData struct
from bool.  So this would not work correctly if there ever is a
checksum version larger than 1.

src/bin/pg_upgrade/controldata.c

@@ -493,7 +493,6 @@ get_control_data(ClusterInfo *cluster, bool live_check)
 				pg_fatal("%d: controldata retrieval problem\n", __LINE__);
 
 			p++;				/* remove ':' char */
-			/* used later for contrib check */
 			cluster->controldata.data_checksum_version = str2uint(p);
 			got_data_checksum_version = true;
 		}

src/bin/pg_upgrade/pg_upgrade.h

@@ -219,7 +219,7 @@ typedef struct
 	uint32		large_object;
 	bool		date_is_int;
 	bool		float8_pass_by_value;
-	bool		data_checksum_version;
+	uint32		data_checksum_version;
 } ControlData;
 
 /*