We can't remove race instrumentation unless there are no calls,
not just no static calls. Closure and interface calls also count.

The problem in issue 29329 is that there was a racefuncenter, an
InterCall, and a racefuncexit.  The racefuncenter was removed, then
the InterCall was rewritten to a StaticCall. That prevented the
racefuncexit from being removed. That caused an imbalance in
racefuncenter/racefuncexit calls, which made the race detector barf.

Bug introduced at CL 121235

Fixes #29329

Change-Id: I2c94ac6cf918dd910b74b2a0de5dc2480d236f16
Reviewed-on: https://go-review.googlesource.com/c/155917
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>