MAINTAINERS: add proppy for google.md

Docker-DCO-1.1-Signed-off-by: Johan Euphrosine <proppy@google.com> (github: proppy)
cleanup all mentions of insert

Docker-DCO-1.1-Signed-off-by: Victor Vieux <vieux@docker.com> (github: vieux)
Merge pull request #6518 from vieux/finish_remove_insert

cleanup all mentions of insert
Merge pull request #6363 from proppy/patch-5

MAINTAINERS: add proppy for google.md