rust/Cargo.toml: Change to "thin local" LTO for faster release builds

"fat" LTO takes much longer to compile than with "thin local" LTO, so
use the Rust release build defaults, which is "thin local" LTO [1-2].

If someone wants to enable "fat" LTO, they can use one of the common
methods to adjust the Rust build process, for example:

  $ cargo build --config 'profile.release.lto=true' --release

or

  $ export CARGO_PROFILE_RELEASE_LTO=true
  $ cargo build --release

[1] https://doc.rust-lang.org/cargo/reference/profiles.html#release
[2] https://doc.rust-lang.org/cargo/reference/profiles.html#lto

Reviewed-by: Steffen Eiden <seiden@linux.ibm.com>
Acked-by: Jan Höppner <hoeppner@linux.ibm.com>
Signed-off-by: Marc Hartmayer <mhartmay@linux.ibm.com>
Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>

rust/Cargo.toml

@@ -26,6 +26,3 @@ unstable_features = "warn"
 unused = "warn"
 unused_import_braces = "warn"
 unused_qualifications = "warn"
-
-[profile.release]
-lto = true