rlc: remove a dead member and three leftover TODO comments

NrRlcAmTxEntity declared txNextAck_ and never used it -- clang reported it as
-Wunused-private-field. The transmission window's real txNextAck_ lives in
RlcSduSlidingWindowTransmissionBuffer, which the entity delegates to.

The other three are comments: two "TODO Auto-generated destructor stub" lines
left behind by the IDE that created the NR PDU classes, and a note in
RlcUmReceptionBuffer::handleSegment speculating that the window-advance path
may leak SDU pointers. It does not -- discardOutsideWindow(), called just
above it, deletes the sduPointer of every entry it drops before erasing it.

Author: avarga

src/simu5g/stack/rlc/am/NrRlcAmTxEntity.h

@@ -48,7 +48,6 @@ class NrRlcAmTxEntity : public RlcAmTxEntityBase
     std::list<omnetpp::cPacket *> controlBuffer_;
     std::string nameEntity_;
     unsigned int sn_ = 0;
-    unsigned int txNextAck_ = 0;
     unsigned int amWindowSize_ = 0;
     unsigned int pduWithoutPoll_ = 0;
     unsigned int byteWithoutPoll_ = 0;

src/simu5g/stack/rlc/am/packet/NrRlcAmDataPdu.cc

@@ -19,7 +19,6 @@ NrRlcAmDataPdu::NrRlcAmDataPdu() : LteRlcDataPdu() {
 }
 
 NrRlcAmDataPdu::~NrRlcAmDataPdu() {
-    // TODO Auto-generated destructor stub
 }
 
 } /* namespace simu5g */

src/simu5g/stack/rlc/um/NrRlcUmDataPdu.cc

@@ -18,7 +18,6 @@ NrRlcUmDataPdu::NrRlcUmDataPdu() {
 }
 
 NrRlcUmDataPdu::~NrRlcUmDataPdu() {
-    // TODO Auto-generated destructor stub
 }
 
 } /* namespace simu5g */

src/simu5g/stack/rlc/um/RlcUmReceptionBuffer.cc

@@ -83,7 +83,6 @@ bool RlcUmReceptionBuffer::handleSegment(uint32_t sn, uint32_t totalLen, uint32_
         discardOutsideWindow();
 
         if (!isWithinWindow(RX_Next_Reassembly)) {
-            // TODO: we may be leaking sdu pointers here
             setNextReassemblyToFirstInWindow();
         }
     }