mhi: dev: net: remove support for recycling buffers

Recycling buffers for downlink transfer is not a supported
feature, hence removing support for it.

CRs-Fixed: 2325839
Change-Id: I097534c027d4c6274ff6d30cfa475fc647ed7b16
Signed-off-by: Sujeev Dias <sdias@codeaurora.org>