fix unit tests in Sandcastle
Summary:
D46232899 fixed a unit test that was failing in CI. Unfortunately this
breaks the same test in Sandcastle due to slightly a different error
message from bash.
Just remove the flaky test, because the very next test in the list does
pretty much the same thing for us anyway.
Test Plan:
```
0 ~/local/openbmc/tools/flashy $ ./build.sh && ./build_dev.sh && go test ./...
ok github.com/facebook/openbmc/tools/flashy (cached)
ok github.com/facebook/openbmc/tools/flashy/checks_and_remediations/bletchley (cached)
ok github.com/facebook/openbmc/tools/flashy/checks_and_remediations/common (cached)
ok github.com/facebook/openbmc/tools/flashy/checks_and_remediations/galaxy100 (cached)
ok github.com/facebook/openbmc/tools/flashy/checks_and_remediations/wedge100 (cached)
ok github.com/facebook/openbmc/tools/flashy/checks_and_remediations/yamp (cached)
? github.com/facebook/openbmc/tools/flashy/flash_procedure [no test files]
ok github.com/facebook/openbmc/tools/flashy/install (cached)
ok github.com/facebook/openbmc/tools/flashy/lib/fileutils (cached)
ok github.com/facebook/openbmc/tools/flashy/lib/flash (cached)
ok github.com/facebook/openbmc/tools/flashy/lib/flash/flashcp (cached)
ok github.com/facebook/openbmc/tools/flashy/lib/flash/flashutils (cached)
ok github.com/facebook/openbmc/tools/flashy/lib/flash/flashutils/devices (cached)
? github.com/facebook/openbmc/tools/flashy/lib/logger [no test files]
ok github.com/facebook/openbmc/tools/flashy/lib/step (cached)
ok github.com/facebook/openbmc/tools/flashy/lib/utils (cached)
ok github.com/facebook/openbmc/tools/flashy/lib/validate (cached)
ok github.com/facebook/openbmc/tools/flashy/lib/validate/image (cached)
ok github.com/facebook/openbmc/tools/flashy/lib/validate/partition (cached)
? github.com/facebook/openbmc/tools/flashy/tests [no test files]
? github.com/facebook/openbmc/tools/flashy/utilities [no test files]
0 ~/local/openbmc/tools/flashy $
```
Reviewed By: mchugh19
Differential Revision: D46450604
fbshipit-source-id: e52594be601d410f936096471fd9595580a92f56