chore: cleanup Cargo.toml and rm perl

* Remove Cargo settings that are identical to the defaults (per Cargo [recommendations](https://doc.rust-lang.org/cargo/reference/manifest.html))
* Fix perl-based method to extract MSRV

(backport <rust-lang#4408>)
(cherry picked from commit d8e39a2)

Author: nyurik

Cargo.toml

@@ -1,21 +1,16 @@
 [package]
 name = "libc"
 version = "0.2.172"
-authors = ["The Rust Project Developers"]
-license = "MIT OR Apache-2.0"
-readme = "README.md"
-edition = "2021"
-repository = "https://github.com/rust-lang/libc"
-homepage = "https://github.com/rust-lang/libc"
-documentation = "https://docs.rs/libc/"
 keywords = ["libc", "ffi", "bindings", "operating", "system"]
 categories = ["external-ffi-bindings", "no-std", "os"]
-build = "build.rs"
 exclude = ["/ci/*", "/.github/*", "/.cirrus.yml", "/triagebot.toml"]
+description = "Raw FFI bindings to platform libraries like libc."
+publish = false # On the main branch, we don't want to publish anything
+authors = ["The Rust Project Developers"]
+edition = "2021"
+license = "MIT OR Apache-2.0"
+repository = "https://github.com/rust-lang/libc"
 rust-version = "1.63"
-description = """
-Raw FFI bindings to platform libraries like libc.
-"""
 
 [package.metadata.docs.rs]
 features = ["extra_traits"]

libc-test/Cargo.toml

@@ -1,16 +1,12 @@
 [package]
 name = "libc-test"
-version = "0.2.155"
-edition = "2021"
+version = "0.1.0"
+description = "A test crate for the libc crate."
+publish = false
 authors = ["The Rust Project Developers"]
+edition = "2021"
 license = "MIT OR Apache-2.0"
-build = "build.rs"
-publish = false
 repository = "https://github.com/rust-lang/libc"
-homepage = "https://github.com/rust-lang/libc"
-description = """
-A test crate for the libc crate.
-"""
 
 [dependencies]
 cfg-if = "1.0.0"