erasure-code: Remove SIMD flavors for jerasure and shec

erasure-code: Remove SIMD flavors for jerasure and shec

By switching to a new gf-complete with SIMD runtime detection, we can now remove all the different flavors of jerasure and shec. This simplifies deployment and configuration of erasure coding, enables hetergenous OSDs, and enables us to take advantage of new performance improvements in jerasure without config/build changes.

This commit removes flavors from cmake, removes ErasureCodePluginSelect___, and fixes unit tests. There is now a single plugin for jerasure and a single plugin for shec.

SIMDExt.cmake was changed so that its a little more generic, and is not polluted with gf-complete specific CFLAG defines. The #define for SIMD instruction were based on gf-complete.

I also added a small init helper for jerasure that has code that was common between jerasure and shec.

Signed-off-by: Bassam Tabbara <bassam.tabbara@quantum.com>