libutils: sharedbuffer test - expect greatness!

This test previously expected failure - a machine which does not have
2GiB of memory. However, while today is becoming the past,
2GiB allocations working is no longer a dream of the future!

Fixes: 186569165
Test: libutils_test
Change-Id: I6a9ed608c0989d415b4e7735b8a451b8928b4083