Remove redundant yet unstable test_spectral_lobpcg_mode

The lobpcg mode is already tested in the test_spectral_clustering test.

LinAlgError was raised when executing test_spectral_lobpcg_mode on some
systems depending on the version of the scipy and LAPACK libraries.
TST: more robust test of dropping in Lars
TST: relax warning class checked in lars
TST: lars tests: more brutal ill-conditionning
ENH: make CD Lasso raise ConvergenceWarning
Merge pull request #3030 from ogrisel/fix-lars-drop-for-good-test-failure

Fix LARS drop for good test failure
DOC: clear up the big elastic net confusion (I hope)

Several users have asked for LogReg w/ E-net (e.g. #3023). Did some
additional copyediting.
Merge pull request #3025 from ogrisel/remove-unstable-lobpcg-test

[MRG] Remove redundant yet unstable test_spectral_lobpcg_mode