I just accidentally discovered how to edit My Maps on the phone. Go into My Tracks and select a track you've recorded, long Press, share with friends, send link, gmail or whichever, and send to yourself. If the track has not already been sent to google it will go thru the send-to-google options.
When you get the mail, click on the link and select to view from the browser. After the map is displayed, at the top there is an icon that looks like a sheet of paper. Press that and you will see the list of all your maps. I was able to choose a map, press edit, select some points and delete them. It's pretty crude, but you can delete maps and do some basic editing.
I had not been able to get to the normal my maps page any other way on the phone's browser, but maybe I just wasn't trying the right url.
Edit: I've only been able to edit the map whose link I sent. After you press the icon to go to the list of maps, scroll to the bottom of the page and, for some reason, it will jump to the page showing all the line segments and markers. You can then select edit and choose items to delete. It gets confused very easily though.
Edit again: I'm an idiot. I have my browser set to mobile mode. All you have to do is go to maps.google.com in not-mobile mode or press the paper icon and switch to classic mode. Then you can select my maps as usual.
