Remove deprecated Warning/Warningf log calls

[travisperson]

Both Warning and Warningf are deprecated in go-log@v1.0.4 and removed in the newer v2. The current use of these deprecated methods impacts the ability to get proper caller information. Logs produced with these methods result in one of two callers inside of the go-log package.

Eg: go-log@v1.0.4/log.go:180, or go-log@v1.0.4/log.go:175.

This makes it more cumbersome to filter through logs when using tools like Kibana where filtering in/out a log line by caller is easier than trying to filter in/out a string of a message. It also makes it hard for anyone not familiar with the libp2p code base to understand where a log is coming from. For warning logs particular knowing the actual caller is important.

[marten-seemann]

We updated to go-log v2 in #294.