Update specifying-dependencies.md

Author: notriddle

src/doc/src/reference/specifying-dependencies.md

@@ -465,11 +465,8 @@ If you want to know which cfg targets are available on your platform, run
 `rustc --print=cfg` from the command line. If you want to know which `cfg`
 targets are available for another platform, such as 64-bit Windows,
 run `rustc --print=cfg --target=x86_64-pc-windows-msvc`.
-If you want to know which cfg targets are used by the release profile,
-add the `-O` parameter.
 
-This same set of values is used throughout the build for all crates in your project,
-so, unlike in your Rust source code,
+Unlike in your Rust source code,
 you cannot use `[target.'cfg(feature = "my_crate")'.dependencies]` to add
 dependencies based on optional crate features.
 Use [the `[features]` section](manifest.md#the-features-section) instead.