[C++] Do not access TZDB if there is no timestamp type

We should not write writerTimeZone or initialize readerTImeZone when there is no timestamp type. For example: https://github.com/apache/orc/blob/513922af6c1d1a07e632a03231d5b546eeafb26e/java/core/src/java/org/apache/orc/impl/WriterImpl.java#L559-L565