pg_upgrade - a function parameter shadows global 'new_cluster'

Hi hackers.

During a recent review of nearby code I noticed that there was a shadowing
of the 'new_cluster' global variable by a function parameter:

Here:
static void check_for_new_tablespace_dir(ClusterInfo *new_cluster);

~~~

It looks like it has been like this for a couple of years. I guess this
might have been found/fixed earlier had the code been compiled differently:

check.c: In function ‘check_for_new_tablespace_dir’:
check.c:381:43: warning: declaration of ‘new_cluster’ shadows a global
declaration [-Wshadow]
check_for_new_tablespace_dir(ClusterInfo *new_cluster)
^
In file included from check.c:16:0:
pg_upgrade.h:337:4: warning: shadowed declaration is here [-Wshadow]
new_cluster;
^

~~~

PSA a small patch to remove the unnecessary parameter, and so eliminate
this shadowing.

Thoughts?

------
Kind Regards,
Peter Smith.
Fujitsu Australia.