pgsql: Remove a few places that attempted to define INT_MAX, SCHAR_MAX,

Log Message:
-----------
Remove a few places that attempted to define INT_MAX, SCHAR_MAX, and
similar constants if they were not previously defined. All these
constants must be defined by limits.h according to C89, so we can
safely assume they are present.

Modified Files:
--------------
    pgsql/contrib/dblink:
        dblink.c (r1.52 -> r1.53)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/dblink/dblink.c.diff?r1=1.52&r2=1.53)
    pgsql/src/backend/utils/adt:
        char.c (r1.44 -> r1.45)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/char.c.diff?r1=1.44&r2=1.45)
        float.c (r1.122 -> r1.123)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/float.c.diff?r1=1.122&r2=1.123)
        int.c (r1.71 -> r1.72)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/int.c.diff?r1=1.71&r2=1.72)
        numutils.c (r1.73 -> r1.74)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/numutils.c.diff?r1=1.73&r2=1.74)