Revert "Set minimum rust version in Cargo.toml"

.github/workflows/test.yml

@@ -38,13 +38,3 @@ jobs:
         with:
           command: test
           args: --verbose --all --no-default-features --features num
-  msrv:
-    steps:
-      - name: Checkout sources
-        uses: actions/checkout@v2
-      - name: Install cargo-msrv
-        uses: baptiste0928/cargo-install@v1.1.0
-        with:
-          crate: cargo-msrv
-      - name: Verify MSRV
-        run: cargo msrv --verify

Cargo.toml

@@ -10,7 +10,6 @@ license = "BSD-3-Clause"
 keywords = ["prolog", "prolog-interpreter", "prolog-system"]
 categories = ["command-line-utilities"]
 build = "build.rs"
-rust-version = "1.57"
 
 [workspace]
 members = ["crates/num-rug-adapter",