adb sideload LMY48G fails

[RBEmerson]

I have a rooted N7 2013 WiFi that isn't accepting the update to LMY48G. I've tried using TWRP and NRT to do an adb sideload. The process fails with

 Verifying current system...
"/system/bin/install-recovery.sh" has unexpected contents.
E:error in /sideload/package.zip
(status 7)

Installation aborted.

Is this because the N7 is rooted or...?

How do I get LMY48G installed and stay rooted?

 

[Laura Knotek]

You'll need to unroot, flash the updated ROM, and then reroot.

Sent from my rooted Nexus 7 (2013) using Tapatalk

 

[RBEmerson]

Sigh... I should have tried that but I decided to reflash LMY47V and then update to LMY48G, and root that. It worked, but meant a full wipe. I backed stuff up, of course, but recovering from a wipe is always a pain.

There is, however, one remaining problem. I'm still getting the OTA update to LMY48G message. If it's to be believed, the OTA update was downloaded and waiting to be installed. And, of course, LMY48G is already in place. How do I get rid of a) the file and b) the message?