Remove `.mailmap` file

[sbrannen]

The .mailmap file currently references @vmware.com email addresses for core committers.

We will need to update that to reflect @broadcom.com email addresses as well, once we switch email addresses used in Git commits to @broadcom.com email addresses.

[snicoll]

FTR this file misses a number of core committers, and I am not sure it is very useful as long as the email address you use is verified in your GitHub account. I am not in that file and I don't really see a difference.

[sdeleuze]

I think we should decide to either remove that file or to fill it to make it extensive.

If possible, preference for the former since we will probably miss some contributors email addresses and since that make our emails an easy target for spams and prevents to use Github no-reply address.

[snicoll]

+1 to remove it.