build: Remove unnecessary build = "build.rs" annotations

src/libprofiler_builtins/Cargo.toml

@@ -1,6 +1,5 @@
 [package]
 authors = ["The Rust Project Developers"]
-build = "build.rs"
 name = "profiler_builtins"
 version = "0.0.0"
 edition = "2018"

src/librustc_attr/Cargo.toml

@@ -3,7 +3,6 @@ authors = ["The Rust Project Developers"]
 name = "rustc_attr"
 version = "0.0.0"
 edition = "2018"
-build = "build.rs"
 
 [lib]
 name = "rustc_attr"

src/librustc_llvm/Cargo.toml

@@ -2,7 +2,6 @@
 authors = ["The Rust Project Developers"]
 name = "rustc_llvm"
 version = "0.0.0"
-build = "build.rs"
 edition = "2018"
 
 [lib]

src/libstd/Cargo.toml

@@ -2,7 +2,6 @@
 authors = ["The Rust Project Developers"]
 name = "std"
 version = "0.0.0"
-build = "build.rs"
 license = "MIT OR Apache-2.0"
 repository = "https://github.com/rust-lang/rust.git"
 description = "The Rust Standard Library"

src/libunwind/Cargo.toml

@@ -2,7 +2,6 @@
 authors = ["The Rust Project Developers"]
 name = "unwind"
 version = "0.0.0"
-build = "build.rs"
 edition = "2018"
 include = [
   '/libunwind/*',

src/tools/error_index_generator/Cargo.toml

@@ -3,7 +3,6 @@ authors = ["The Rust Project Developers"]
 name = "error_index_generator"
 version = "0.0.0"
 edition = "2018"
-build = "build.rs"
 
 [dependencies]
 rustdoc = { path = "../../librustdoc" }