The two diodes serve different purposes. The first one prevents C1 from draining if power is temporarily removed from JP1. The second one prevents the condition where Vout > Vin (by more than one diode drop). This may be required if there is a lot of capacitance on Vout. LDO's are normally designed for the condition where Vout < Vin. If this is reversed, there could be large currents that flow back into the LDO and they could cause some damage. Did you read the datasheet for the LDO?
It's a two-diode package for convenience, but the diodes serve two different functions:
The one on the left is providing reverse-voltage protection for the regulator. It keeps current from flowing if the connections to
JP1are accidentally swapped.
The one on the right protects the regulator from excess positive
VINdifferential voltage. Many regulators can be damaged if
VINby any significant margin, and the diode makes sure that
VINis no more than one diode drop below
VOUT, even if the input power is removed.