THRIFT-5338: Remove lib/go/thrift/go.mod

Client: go

Having it under a subdirectory has some unexpected consequences, so
remove it for now. Another PR will be open up later to add it back to
the root directory.
diff --git a/lib/go/thrift/go.mod b/lib/go/thrift/go.mod
deleted file mode 100644
index 430c255..0000000
--- a/lib/go/thrift/go.mod
+++ /dev/null
@@ -1,3 +0,0 @@
-module github.com/apache/thrift/lib/go/thrift
-
-go 1.14