Removed existing JPA implementations and tests.

Removed existing JPA implementations and tests from the initial code drop so that the user can create them during "Step 3: Storing Order Data Using the Java Persistence API (JPA)" of the tutorial.
Removed existing MongoDB implementations and tests.

Removed existing MongoDB implementations and tests from the initial code drop so that the user can create them during "Step 2: Storing Menu Data Using MongoDB" of the tutorial.