aconfig: reduce number of #[cfg(feature = "cargo")] uses

Group statements with identical #[cfg(feature = "cargo")] attributes in
the same block. This reduces repetition and makes the code easier to
read and less error prone.

Bug: 284779868
Test: atest aconfig.test
Change-Id: Iebdcd20e7cd22cb641424a1af594f5c9ac57b623