libmsc: use smpp34_tlv_for_each() to avoid suboptimal TLV handling

submit_to_sms() now handles two TLVs, so find_tlv() is suboptiomal and
it can be removed, since it would result in two passes on the TLV list.
Use new smpp34_tlv_for_each() helper to iterate over the list of TLVs
that is available since I446929feed049d0411e1629ca263e2bc41f714cc.

Change-Id: I53a65164a6cc4abc6bf57d9a8dc275cf21c90222
1 file changed