Add cdma_3waycall_flash_delay key to CarrierConfig

Add KEY_CDMA_3WAYCALL_FLASH_DELAY_INT and default value to
CarrierConfigManager, and remove the references to the old config in
core/res/res/values/[config.xml/symbols.xml]

Bug: 29873049
(cherry picked from commit bd3f2a7e)

Change-Id: If3f658281e62d1c2669f862c6c3812a7437c6dce