docs(ng-update): Update CHANGELOG.md
docs(ng-update): Update CHANGELOG.md

Remove 6.1.0 header and add note about migration schematic.

(cherry picked from commit 02b122df2c7b5e31b8b17aff07d5e9153a599bd9)

# Conflicts:
#	CHANGELOG.md

Infragistics/zero-blocks,Infragistics/zero-blocks,Infragistics/zero-blocks