Update .gitignore

The SDK used to generate Dockerfile in the chaincode folder so
it can send it in the deploy transaction. But that's not being
done any longer due to https://gerrit.hyperledger.org/r/#/c/5427

Accordingly .gitignore should not include the generated Dockerfile
entries any longer.

Change-Id: I4425c48e06f210df4c4b19ee2d2c8e16fbe1896c
Signed-off-by: Jim Zhang <jzhang@us.ibm.com>

.gitignore

@@ -9,8 +9,6 @@ fabric-ca-client/lib/Config.js
 fabric-ca-client/lib/Remote.js
 fabric-ca-client/lib/hash.js
 fabric-ca-client/lib/impl/*
-test/fixtures/src/github.com/example_cc/Dockerfile
-test/fixtures/src/github.com/marbles_cc/Dockerfile
 npm-shrinkwrap.json
 npm-debug.log
 tmp