Removes redundant imports

[brooksprumo]

Problem

clippy nightly throws new lints for redundant imports. For example:

warning: the item `Read` is imported redundantly
 --> programs/bpf_loader/gen-syscall-list/build.rs:5:37
  |
5 |         io::{prelude::*, BufWriter, Read},
  |              ----------             ^^^^
  |              |
  |              the item `Read` is already imported here
  |
  = note: `#[warn(unused_imports)]` on by default

Summary of Changes

Remove 'em.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.9%. Comparing base (e027a8b) to head (13ac3e1).
Report is 18 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff            @@
##           master     #193    +/-   ##
========================================
  Coverage    81.8%    81.9%            
========================================
  Files         838      837     -1     
  Lines      226389   226502   +113     
========================================
+ Hits       185342   185548   +206     
+ Misses      41047    40954    -93