Update 2.7 release notes; remove 2.6.2 release notes

All the fixes that went into the stable-2.6 branch have been
merged into stable-2.7 and released in version 2.7.

Update the 2.7 release notes with these fixes, and remove the
2.6.2 release notes which is now redundant.

Change-Id: I6117d31ef0ac00c03d1c59839476efc05b98bb30
2 files changed