Remove the `time-passes` profiling mode.
I recently realized that the `time-passes` mode can be easily emulated
with the `eprintln` mode. Instead of running this:
```
collector profile_local time-passes $RUSTC
```
you can run this for the same effect:
```
RUSTFLAGS=-Ztime-passes collector profile_local eprintln $RUSTC
```
The `RUSTFLAGS` approach is more flexible, and can be used for other
profiling modes built into the compiler: `-Zhir-stats`, `-Zmeta-stats`,
etc.
So this commit removes the `time-passes` support.
