Simplify docsrs feature usage

- Don't instruct docs.rs to set it, it does so by default now:
  https://github.com/rust-lang/docs.rs/pull/2390
- Because of that, check-cfg also recognizes it and does not need
  extra configuration either.

crates/ruma-html/Cargo.toml

@@ -12,7 +12,6 @@ rust-version = { workspace = true }
 
 [package.metadata.docs.rs]
 all-features = true
-rustdoc-args = ["--cfg", "docsrs"]
 
 [features]
 matrix = ["dep:ruma-common"]

crates/ruma-html/build.rs

@@ -1,6 +0,0 @@
-fn main() {
-    // Prevent unnecessary rerunning of this build script
-    println!("cargo:rerun-if-changed=build.rs");
-    // Prevent nightly CI from erroring on docsrs attributes
-    println!("cargo:rustc-check-cfg=cfg(docsrs)");
-}