Building __DATE__/__TIME__ into the binaries means that every build will
create different binaries, even if all the sources are identical. This
also means that any libraries including this one will need to be patched
during every OTA.

Nothing appears to use the build_date/build_time fields, so just replace
them with empty strings.

Bug: 24204119
Change-Id: I9543eb388a1e8ab9284df9035a62fc8942cdc082