[TEST] DisabledFieldDataFormatTests assumes a single replica.
Throw exception if decay is requested for a field with multiple values

closes #3960
Revert "Throw exception if decay is requested for a field with multiple values"

This reverts commit 95d781510f9ec66b6615df4e26ccc18da9c2b155.

see https://github.com/elasticsearch/elasticsearch/issues/3960#issuecomment-41279373
Update keyword-repeat-tokenfilter.asciidoc