docs.rs docs patch: token_program override example

[fedorerd]

I've been working with interfaces recently and this example was very confusing.

1. Updated imports to imports from anchor_spl::token_interface

2. I removed Box<> because docs.rs currently displays them incorrectly for some reason:
   
   Boxing accs here isn't necessary for educational purposes of this example, and hopefully removing them will fix what docs.rs builds.

Attaching link to this example on docs.rs so u could see how confusing it is right now:
https://docs.rs/anchor-lang/latest/anchor_lang/derive.Accounts.html#:~:text=%23%5Baccount(*%3A%3Atoken_program%20%3D%20%3Ctarget_account%3E)%5D

[vercel]

@fedorerd is attempting to deploy a commit to the coral-xyz Team on Vercel.

A member of the Team first needs to authorize it.

[acheroncrypto]

Thanks!