[Reproducers] Stop recording instead of deallocating

The command interpreter holds a pointer to a DataRecorder. After
generating the reproducer, we deallocated all the DataRecorders, causing
the command interpreter to hold a non-null reference to an invalid
object.

This patch changes the behavior of the command provider to stop the
DataRecorders when a reproducer is generated, rather than deallocating
them.

llvm-svn: 355940