DOC: user guide compat with osmnx 2.0

[martinfleis]

They renamed one level of the multiindex. This seems to be the only place where we explicitly drop that one. The rest is probably going to work fine.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.1%. Comparing base (4037c70) to head (a45c836).
Report is 96 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##            main    #669     +/-   ##
=======================================
+ Coverage   97.4%   98.1%   +0.8%     
=======================================
  Files         26      40     +14     
  Lines       4328    7206   +2878     
=======================================
+ Hits        4214    7072   +2858     
- Misses       114     134     +20     

see 1 file with indirect coverage changes

---- 🚨 Try these New Features:

• Flaky Tests Detection - Detect and resolve failed and flaky tests