cmd/protoc-gen-go/testdata: remove go.mod file

In the distant past this was necessary because:
1) the generated code depended on github.com/golang/protobuf,
but now it doesn't.
2) protoc-gen-go-grpc had a dependency on google.golang.org/grpc,
and the seperate go.mod file allowed us to isolate the dependency,
but that binary doesn't exist here anymore.

Drop the go.mod file for cmd/protoc-gen-go/testdata.

Change-Id: I7341d78dc346bd82e5c68ed48cee3275b6296249
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/220502
Reviewed-by: Damien Neil <dneil@google.com>

.gitignore

diff --git a/.gitignore b/.gitignore
index 6e3f595..d559d39 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,10 +1,6 @@
 /.cache
 /.gocache
 /bin
-/cmd/protoc-gen-go/protoc-gen-go
-/cmd/protoc-gen-go/testdata/go.sum
-/cmd/protoc-gen-go-grpc/protoc-gen-go-grpc
-/cmd/protoc-gen-go-grpc/testdata/go.sum
 /vendor
 /internal/fuzz/wire/fuzz-fuzz.zip
 

cmd/protoc-gen-go/testdata/go.mod

diff --git a/cmd/protoc-gen-go/testdata/go.mod b/cmd/protoc-gen-go/testdata/go.mod
deleted file mode 100644
index 37f2934..0000000
--- a/cmd/protoc-gen-go/testdata/go.mod
+++ /dev/null
@@ -1,10 +0,0 @@
-module google.golang.org/protobuf/cmd/protoc-gen-go/testdata
-
-go 1.9
-
-require (
-	github.com/golang/protobuf v1.4.0-rc.1
-	google.golang.org/protobuf v1.0.0
-)
-
-replace google.golang.org/protobuf => ../../..