Remove string_number_conversions.h from payload_generation_config.cc am: 333a619cce

Original change: https://android-review.googlesource.com/c/platform/system/update_engine/+/3309079

Change-Id: Id5577a41e4d20d0c85b1d0745d72284bd02ae29f
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>