Remove semver and sha2 re-exports

These re-exports appear to be unnecessary, and doesn't have any impact on code that rely on the `inventory` module (and uses these feature- trait implementation). Also see related prior discussion here Malax/inventory#2 (comment).

The `semver` and `sha2` modules only contain implementations of public traits, so I don't think we need to re-export those (unlike bringing for instance a function or struct in to scope).

If I understand how trait implementations work correctly, it doesn't matter where an implementation lives (only the visibility of the trait and the type it's implemented for is relevant) - in other words, the implementation will be available to any code that can access both the trait and the type, even across crate binaries.

libherokubuildpack/src/inventory.rs

@@ -8,13 +8,6 @@ mod semver;
 mod sha2;
 mod unit;
 
-#[allow(unused_imports, unreachable_pub)]
-#[cfg(feature = "semver")]
-pub use semver::*;
-#[allow(unused_imports, unreachable_pub)]
-#[cfg(feature = "sha2")]
-pub use sha2::*;
-
 use crate::inventory::artifact::{Arch, Artifact, Os};
 use crate::inventory::checksum::Digest;
 use crate::inventory::version::ArtifactRequirement;