Remove some outdated info from readme

cpp/README.md

@@ -68,7 +68,6 @@ For the first layer of the wrapper, built using Cargo:
 - CXX doesn't provide integration between Rust's `Option<_>` and C++'s `std::optional<T>`, so sentinel values are used to communicate the absence of a value in the wrapper's API:
     - For `Option<&str>`, `None` is represented using an empty string, which is how it's already done for many metadata object fields in the C++ implementation of libloot.
     - For `Option<f32>`, `None` is represented using `NaN`, since the C++ implementation of libloot's public API already says that `NaN` values get converted to `None`.
-    - Plugin CRCs (which are `Option<u32>` in Rust) are represented as `int64_t`, with `-1` representing `None`, since all `uint32_t` values are possibly valid CRCs.
 - All Rust errors are converted to `::rust::Error` exceptions that have a `what()` string that is the concatenation of the error's display string and all its recursive source error display strings. For some errors the `what()` string also includes some data that is parsed by the wrapper's second layer to differentiate certain error types.
 
 For the ABI-compatible second layer of the wrapper, built using CMake: