alloc.[ch]: remove alloc_report() function

alloc.[ch]: remove alloc_report() function

The alloc_report() function has been orphaned since its introduction
in 855419f764a (Add specialized object allocator, 2006-06-19), it
appears to have been used for demonstration purposes in that commit
message.

These might be handy to manually use in a debugger, but keeping them
and the "count" member of "alloc_state" just for that doesn't seem
worth it.

Signed-off-by: Ævar Arnfjörð Bjarmason <redacted>
Signed-off-by: Junio C Hamano <redacted>