Fix multiple build target warnings on examples

[sragss]

When running cargo build -p jolt-core the following build warnings appear:

warning: /Users/sragsdale/Documents/Code/a16z/jolt/examples/sha3-ex/guest/Cargo.toml: file `/Users/sragsdale/Documents/Code/a16z/jolt/examples/sha3-ex/guest/src/lib.rs` found to be present in multiple build targets:
  * `lib` target `sha3-guest`
  * `bin` target `guest`
warning: /Users/sragsdale/Documents/Code/a16z/jolt/examples/sha3-chain/guest/Cargo.toml: file `/Users/sragsdale/Documents/Code/a16z/jolt/examples/sha3-chain/guest/src/lib.rs` found to be present in multiple build targets:
  * `lib` target `sha3-chain-guest`
  * `bin` target `guest`
warning: /Users/sragsdale/Documents/Code/a16z/jolt/examples/multi-function/guest/Cargo.toml: file `/Users/sragsdale/Documents/Code/a16z/jolt/examples/multi-function/guest/src/lib.rs` found to be present in multiple build targets:
  * `lib` target `multi-function-guest`
  * `bin` target `guest`
warning: /Users/sragsdale/Documents/Code/a16z/jolt/examples/sha2-ex/guest/Cargo.toml: file `/Users/sragsdale/Documents/Code/a16z/jolt/examples/sha2-ex/guest/src/lib.rs` found to be present in multiple build targets:
  * `lib` target `sha2-guest`
  * `bin` target `guest`
warning: /Users/sragsdale/Documents/Code/a16z/jolt/examples/sha2-chain/guest/Cargo.toml: file `/Users/sragsdale/Documents/Code/a16z/jolt/examples/sha2-chain/guest/src/lib.rs` found to be present in multiple build targets:
  * `lib` target `sha2-chain-guest`
  * `bin` target `guest`
warning: /Users/sragsdale/Documents/Code/a16z/jolt/examples/alloc/guest/Cargo.toml: file `/Users/sragsdale/Documents/Code/a16z/jolt/examples/alloc/guest/src/lib.rs` found to be present in multiple build targets:
  * `lib` target `alloc-guest`
  * `bin` target `guest`
warning: /Users/sragsdale/Documents/Code/a16z/jolt/examples/fibonacci/guest/Cargo.toml: file `/Users/sragsdale/Documents/Code/a16z/jolt/examples/fibonacci/guest/src/lib.rs` found to be present in multiple build targets:
  * `lib` target `fibonacci-guest`
  * `bin` target `guest`
warning: /Users/sragsdale/Documents/Code/a16z/jolt/examples/stdlib/guest/Cargo.toml: file `/Users/sragsdale/Documents/Code/a16z/jolt/examples/stdlib/guest/src/lib.rs` found to be present in multiple build targets:
  * `lib` target `stdlib-guest`
  * `bin` target `guest`
warning: /Users/sragsdale/Documents/Code/a16z/jolt/examples/collatz/guest/Cargo.toml: file `/Users/sragsdale/Documents/Code/a16z/jolt/examples/collatz/guest/src/lib.rs` found to be present in multiple build targets:
  * `lib` target `collatz-guest`
  * `bin` target `guest`