Remove check for severe-level log duplicates from LocalGcdHelper

[ajkannan]

As of now, gcd.sh will log some messages (i.e. "too much contention on entities") at both the INFO and SEVERE level. When this is fixed in the next gcd release, we can remove the duplication check from LocalGcdHelper.

[ajkannan]

The original issue is obsolete because #250 doesn't remove duplicates. We can close this issue once we upgrade to the next gcd.sh version in LocalGcdHelper, which will remove duplicates.

[ajkannan]

This should be fixed in version 0.1.7 of gcloud-java-datastore, since we upgraded to a new gcd script.