Revert "xds/googlec2p: use xdstp names for LDS (#6949)"

[apolcyn]

This reverts commit 3aafa84.

As described in https://github.com/grpc/proposal/blob/master/A47-xds-federation.md#bootstrap-config-changes, client_listener_resource_name_template inside the authority map should default to xdstp://<authority_name>/envoy.config.listener.v3.Listener/%s, so #6949 shouldn't be necessary.

cc @arvindbr8

RELEASE NOTES: none

[codecov]

Codecov Report

Merging #6964 (f802b97) into master (03e76b3) will increase coverage by 0.11%.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6964      +/-   ##
==========================================
+ Coverage   83.70%   83.82%   +0.11%     
==========================================
  Files         288      288              
  Lines       30921    30920       -1     
==========================================
+ Hits        25883    25919      +36     
+ Misses       3976     3950      -26     
+ Partials     1062     1051      -11     

Files	Coverage Δ
xds/googledirectpath/googlec2p.go	84.52% <100.00%> (-0.19%)	⬇️

... and 23 files with indirect coverage changes

[arvindbr8]

I'm inclined to leaving it as is. To me it is evident that the resource name template uses xdstp://<authority_name>/envoy.config.listener.v3.Listener/%s only if I remember the gRFC percept or I follow the code to see that there is a default applied.
WDYT?

[apolcyn]

My concern is that this is inconsistent with other languages.

In the worst case, it could potentially mask other inconsistencies with the other langs.

If nothing else, this would cause some confusion when reading the google-c2p resolver code - since the Go c2p resolver would be generating a unique bootstrap config relative to the other languages.

[arvindbr8]

SGTM