Remove obsolete function pageChecksumBufferTest().

This function made validation faster in Perl because fewer calls (and buffer transformations) were required when all checksums were valid.

In C calling pageChecksumTest() directly is just as efficient so there is no longer a need for pageChecksumBufferTest().

test/define.yaml

@@ -323,7 +323,7 @@ unit:
 
       # ----------------------------------------------------------------------------------------------------------------------------
       - name: page-checksum
-        total: 3
+        total: 2
 
         coverage:
           postgres/pageChecksum: full