In the api changelog:
it states:
Apps which use API services like
CommitService,ContentServiceandRefServicewill be unaffected. Additionally, ourCommandBuilderAPI (includingGitCommandBuilderFactoryandGitScmCommandBuilder) is also unaffected, continuing to allow app developers the ability to build and execute arbitrarygitcommands. Going forward, our APIs will be the only available mechanism for interacting with repository contents.
My read of that is that you should still be able to use GitScmCommandBuilder, but I don't see any path:
com.atlassian.bitbucket.scm.git
available, which is where this is supposed to live.