need a String::EraseAllChars-alike for OUStringBuffer
need a String::EraseAllChars-alike for OUStringBuffer

Change-Id: I189c08a4100b32b16527ae40df3a9125bf78be88

JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core