libcameraservice: Disable external provider for legacy HAL1

 * The external camera provider was introduced by commit:
    Camera: listen to external camera provider
    Change-Id: I051c77d7b0fe1e0e3b3b2461e7f8da9bd91a440c

 * Enabling this on legacy HAL1 devices crashes the
    kernel video driver, while serving no purpose

 * Makes the original commit depend on the variable
    TARGET_HAS_LEGACY_CAMERA_HAL1 not being true

Change-Id: I954b550e3de848c2c315713f4340697c03878c3e