Revert "add manifest rust-version"

This reverts commit 8341045.

Superseded by f1a9754

Author: jordens

.github/workflows/ci.yml

@@ -21,7 +21,7 @@ jobs:
 
         include:
           # Test MSRV
-          - rust: 1.51.0  # sync with manifest rust-version
+          - rust: 1.51.0
             TARGET: x86_64-unknown-linux-gnu
 
           # Test nightly but don't fail

Cargo.toml

@@ -4,7 +4,6 @@ categories = ["no-std"]
 description = "serde-json for no_std programs"
 documentation = "https://docs.rs/serde-json-core"
 edition = "2018"
-rust-version = "1.51.0"  # sync with CI
 keywords = ["serde", "json"]
 license = "MIT OR Apache-2.0"
 name = "serde-json-core"