Remove hacks supporting old Eigen when it is bumped to 3.2.5

[Jan Blechta]

When required version of Eigen is bumped to 3.2.5, commit 29f335e2fb411f70ac6dbcb761b52cbe5ad3d9ac which avoid using CG on unsymmetric matrix (which is justifiable there) and swithches to GMRES (or BiCGstab) may be reverted and CG can be used again.

[Jan Blechta]

Also 1e77181 and 491feb9.

[Jan Blechta]

And b4dc3ca.

[Jan Blechta]

Also 218a742.

[Jan Blechta]

Only Eigen 3.2.0 is still required.

[Anders Logg (Chalmers)]

Removing milestone: 1.7 (automated comment)

[Prof Garth Wells]

Ubuntu 16.04 has Eigen3 version 3.3~beta1-2. Can we bump the required version and close this issue?

[Jan Blechta]

No. This issue will be close after compatibility hacks for old Eigen are removed. See the description. When the version is bumped this issue should be scheduled for the earliest release.

[Prof Garth Wells]

ok, so let's bump the version so this can be closed.

[Prof Garth Wells]

Version bumped in 90d963971b1ff7f9c96b9c5d364482e5616afd09.

[Prof Garth Wells]

Closing this issue because Eigen version has been bumped.

Left some solvers as BiCGSTAB because I'm not sure we can be confident of what preconditioners will do to non-symmetric operator. Should really just make sure operator is symmetric when using CG.