Remove chunkSize and initialize from erasure coder

Per discussion in HDFS-8347, we need to support encoding/decoding variable width units data instead of predefined fixed width like chunkSize. Have this issue to remove chunkSize in the general raw erasure coder API. Specific coder will support fixed chunkSize using hard-coded or specific schema customizing way if necessary, like HitchHiker coder.

Update: per discussion in this issue, this will also remove initialize method from erasure coders. The necessary initialization work will be done in constructors.