[md][couplingmanager] Fix nullptr initialization of problem

Remove unncessary capture for init lambda functions
5 jobs for !2874 with fixup/couplingmanager-nullptr-init-problem
latest detached
Status Name Job ID Coverage
  Trigger
passed full-dune-latest-release-clang

passed full-dune-latest-release-gcc

passed full-dune-master-gcc

passed minimal-dune-latest-release-gcc

 
  Downstream Modules
passed trigger lecture