TST: linalg: add more comprehensive test cases for linalg funcs

Also remove TestCase subclassing, so that generator tests work.  Also
fix bugs in the existing generator tests that were not actually run
previously.
BUG: linalg: use correct BLAS incx convention in xCOPY
BUG: linalg: fix eigvalsh return type (always real-valued)
MAINT: linalg: strip out unused gufuncs_linalg code

Some of the functions removed were untested, and apparently did not
function correctly (cholesky_up, inner1d, maybe more).
TST: linalg: add slightly bigger test case + don't catch KeyboardInterrupt
TST: linalg: better rtol choice
Merge pull request #3881 from charris/backport-1.8-3880

Backport 1.8 3880