Fix clippy error useless_vec

[p-alik]

Removed useless vec! macro

• Issue

14:40 $ cargo clippy --all
    Checking eif_loader v0.1.0 (/tmp/aws-nitro-enclaves-cli/eif_loader)
    Checking enclave_build v0.1.0 (/tmp/aws-nitro-enclaves-cli/enclave_build)
    Checking driver-bindings v0.1.0 (/tmp/aws-nitro-enclaves-cli/driver-bindings)
    Checking vsock-proxy v0.1.0 (/tmp/aws-nitro-enclaves-cli/vsock_proxy)
    Checking nitro-cli v1.2.2 (/tmp/aws-nitro-enclaves-cli)
error: useless use of `vec!`
   --> src/enclave_proc_comm.rs:193:22
    |
193 |     let mut events = vec![EpollEvent::empty(); 1];
    |                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: you can use an array directly: `[EpollEvent::empty(); 1]`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#useless_vec
note: the lint level is defined here
   --> src/enclave_proc_comm.rs:4:9
    |
4   | #![deny(warnings)]
    |         ^^^^^^^^
    = note: `#[deny(clippy::useless_vec)]` implied by `#[deny(warnings)]`

error: could not compile `nitro-cli` (lib) due to previous error

Description of changes:

The only commit of the PR contains a little code amendment with respect to useless_vec

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