remove _DARWIN_USE_64_BIT_INODE

I was testing autoconf git master and wanted to give some feedback.

In PostgreSQL's configure.in (yeah, we should rename that), we have a 
workaround hack that disables AC_SYS_LARGEFILE's defining of 
_DARWIN_USE_64_BIT_INODE, because that (a) activates some bugs in Mac OS 
X 10.5, and (b) is no longer necessary in >=10.6 (see [0]).  Rather than 
find a new workaround hack, I figured perhaps it would be better to 
remove the define altogether, since it might have been problematic to 
begin with and the OS version in question is more than 10 years out of 
support now.


[0]: 
https://www.postgresql.org/message-id/flat/3894.1388303301%40sss.pgh.pa.us#5791f19e7696d66b4e19a841cc9740e6