cargo: switch from proc-macro pin-project to declarative pin-project-lite

In our simple use cases they both should generate the same code, see
[0] for notable differences. While we cannot drop proc-macro due to
that switch, all of our dependencies that use pinning already use
pin-project-lite, so this allows us to drop a whole crate in general
while not loosing anything.

[0]: https://github.com/taiki-e/pin-project-lite#pin-project-vs-pin-project-lite

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>

Cargo.toml

@@ -68,8 +68,6 @@ openssl = "0.10"
 pam = "0.7"
 pam-sys = "0.5"
 percent-encoding = "2.1"
-pin-utils = "0.1.0"
-pin-project = "1.0"
 regex = "1.2"
 rustyline = "7"
 serde = { version = "1.0", features = ["derive"] }