I find this to be very true XD cant tell you how many times I've lost a snipe kill due to the damn round messages.
But if you really want to remove the text then you should look into .rez modding/editing. I think that HUD message is actually an image (correct me if I'm wrong). Alas all you would need to do is crack open the corresponding UI_* .rez file, navigate to whatever .DTX that particular HUD image is and edit ti to be transparent. Reinject and your golden!
You can find .rez modding tutorials in the .rez modding tutorial section here.
Some of the tutorials are outdated but should still provide you with the basic knowledge and tools needed for .rez modding.
Alright now I feel kinda stupid :3 I reread your post, the message you see at the start of the match with the map name is probably part of the code itself and NOT a .dtx For that I am unable to help, I work on .rez mods and not the code
PS: However, I did do some .rez extracting and found the "Round Start" image (The one for fireteam) in UI_HUD_MESSAGE\EFFECT\ROUNDSTART.DTX