Revert "go: Define a bytePool for TRichTransport"

This reverts commit 344498b67f42af38118cc250b0b1ec212f09d927.

In our extreme case this actually made things worse. On 30s cpu
profiles, although mallocgc reduced from 27.13s to 26.30s, the byte pool
itself costed 11.9s. Looking at writeByte and readByte, writeByte
increased from 3.69s to 5.89s, and readByte increased from 11.36s to
16.09s.