tests/check/pipelines/: Totally remove the UINT64_CONSTANT macro, doesn't appear to be needed or available.

Original commit message from CVS:
2006-01-30  Andy Wingo  <wingo@pobox.com>

* tests/check/pipelines/vorbisenc.c (TIMESTAMP_OFFSET):
* tests/check/pipelines/theoraenc.c (TIMESTAMP_OFFSET): Totally
remove the UINT64_CONSTANT macro, doesn't appear to be needed or
available.