Fix Sphinx privacy leak

[t-bast]

This PR fixes two small issues:

• Sphinx privacy leak
• Recipient should not collect fees

[codecov-io]

Codecov Report

Merging #1247 into master will increase coverage by 0.15%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #1247      +/-   ##
==========================================
+ Coverage      77%   77.15%   +0.15%     
==========================================
  Files         142      142              
  Lines        9902     9903       +1     
  Branches      389      392       +3     
==========================================
+ Hits         7625     7641      +16     
+ Misses       2277     2262      -15

Impacted Files	Coverage Δ
...src/main/scala/fr/acinq/eclair/crypto/Sphinx.scala	100% <100%> (ø)	⬆️
.../scala/fr/acinq/eclair/payment/PaymentPacket.scala	90.9% <100%> (ø)	⬆️
...q/eclair/blockchain/electrum/ElectrumWatcher.scala	50% <0%> (-1.73%)	⬇️
...c/main/scala/fr/acinq/eclair/channel/Channel.scala	83.56% <0%> (-0.1%)	⬇️
...nq/eclair/blockchain/electrum/ElectrumWallet.scala	81% <0%> (+0.25%)	⬆️
...src/main/scala/fr/acinq/eclair/router/Router.scala	92.71% <0%> (+0.71%)	⬆️
...nq/eclair/blockchain/electrum/ElectrumClient.scala	74% <0%> (+0.72%)	⬆️
.../acinq/eclair/blockchain/bitcoind/ZmqWatcher.scala	96.22% <0%> (+3.77%)	⬆️
...clair/blockchain/electrum/ElectrumClientPool.scala	78.49% <0%> (+4.3%)	⬆️
...cinq/eclair/blockchain/bitcoind/zmq/ZMQActor.scala	94.87% <0%> (+5.12%)	⬆️
... and 1 more