See Older Intel Graphics To Drop From OpenGL 2.1 To 1.4 On Linux for more of the background to this story. This change just affects i915 to pre-i965 hardware by dropping OpenGL 2.0 by default due to Chrome and other applications making use of really slow code-paths when using the GL2 extensions on this old hardware that doesn't have adequate OpenGL 2 capabilities. So there's a better out-of-the-box experience by actually dropping the exposed OpenGL version back to v1.4.
But the latest Mesa code will at least continue to expose OpenGL ES 2.0 and the OpenGL 2 support can be restored if setting the fragment_shader and stub_occlusion_query options.
The change is present for Mesa 17.1.