fmt_test.go: remove redundant type conversion

Change-Id: I700d2b25c91938caa2b90dc3cb0cc2d94a3e0daf
GitHub-Last-Rev: 6d7d0646a4ca3a2a493459c914d397e3de27f9ea
GitHub-Pull-Request: golang/xerrors#4
Reviewed-on: https://go-review.googlesource.com/c/xerrors/+/428985
Reviewed-by: Heschi Kreinick <heschi@google.com>
Run-TryBot: Heschi Kreinick <heschi@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Heschi Kreinick <heschi@google.com>
Reviewed-by: Damien Neil <dneil@google.com>

fmt_test.go

diff --git a/fmt_test.go b/fmt_test.go
index 1e3c060..99d945f 100644
--- a/fmt_test.go
+++ b/fmt_test.go
@@ -485,7 +485,7 @@
 	err error
 }
 
-func (e adapted) Error() string { return string(e.msg) }
+func (e adapted) Error() string { return e.msg }
 
 func (e adapted) Format(s fmt.State, verb rune) {
 	xerrors.FormatError(e, s, verb)