Remove unnecessary getRow overloads in HRS

HRS currently contains:

public RowResult getRow(final byte [] regionName, final byte [] row, final long ts)

public RowResult getRow(final byte [] regionName, final byte [] row, final byte [][] columns)

public RowResult getRow(final byte [] regionName, final byte [] row, final byte [][] columns, final long ts)

The first two call the last one which calls HR.getFull.

Changes will be made to HTable to map all getRow calls to a single getRow HRS method.