Remove compiler version support from readme

Superseded by `rust-version` metadata in Cargo.toml.

Author: dtolnay

README.md

@@ -34,7 +34,6 @@ macros.
 quote = "1.0"
 ```
 
-*Version requirement: Quote supports rustc 1.71 and up.*<br>
 [*Release notes*](https://github.com/dtolnay/quote/releases)
 
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