Eigen solvers cleaned up

4 jobs for feature/eigen_backend in 20 minutes and 2 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Test
passed #6515
debian:10 clang-6-libcpp-17

00:20:01

passed #6514
debian:10 gcc-8-17

00:13:06

passed #6516
debian:9 gcc-6-14

00:12:40

passed #6517
ubuntu:18.04 clang-6-17

00:19:48