Fix Linear Map for Cargo 1.71

[AdinAck]

Motivation

In the latest version of Cargo the implementation of Drop for linear map does not compile.

Changes

Revert Drop impl to previous implementation.

[birkenfeld]

This patch isn't correct. Like the new code says, Vec already implements Drop, so your change will call drop() twice on the contents. Look at this example:

struct S;

impl Drop for S {
    fn drop(&mut self) {
        println!("dropped an S");
    }
}

fn main() {
    let mut v = heapless::LinearMap::<&str, S, 5>::new();
    v.insert("a", S).ok().unwrap();
}

It will print "dropped an S" twice with the PR.

Just removing the drop(&self.buffer) is enough IMO.

[AdinAck]

I did notice it continued to work when the entire Drop impl was removed, didn't realize it actually is not necessary. I will just remove it then, thanks.

[newAM]

There seems to be something wrong with the commits here, perhaps a git revert gone wrong?

I made a separate PR to fix in #388

[AdinAck]

cool yeah this PR desperately needed a rebase

[Dirbaio]

fixed in #388