[webrtc-pc] Duplicate definitions errors (following udpate to respec 19.6.0)

vivienlacourba has just created a new issue for https://github.com/w3c/webrtc-pc:

== Duplicate definitions errors (following udpate to respec 19.6.0) ==
Hi, following code changes in respec and the webrtc-respec-ci toolchain I had to move webrtc-pc to a newer respec release.

This new respec release (19.6.0) now reports new errors such as:
```
Errors
    Duplicate definitions of 'peeridentity' at: 1, 2, 3.
    Duplicate definitions of 'closed' at: 1, 2, 3, 4.
    (...)
```
And one warning:
```
Warnings
    Found linkless element for 'rtcrtpsender' with text 'getparameters' but no matching <dfn>.
```
See: https://w3c.github.io/webrtc-pc/

I am hoping one of the editor can look at this and my sincere apologies for the trouble. Thx.

Please view or discuss this issue at https://github.com/w3c/webrtc-pc/issues/1781 using your GitHub account