misc: Remove redundant "use" imports

With the nightly toolchain (2024-02-18) cargo check will flag up
redundant imports either because they are pulled in by the prelude on
earlier match.

Remove those redundant imports.

Signed-off-by: Rob Bradford <rbradford@rivosinc.com>

vmm/src/lib.rs

@@ -2035,7 +2035,7 @@ mod unit_tests {
     use crate::config::DebugConsoleConfig;
     use config::{
         ConsoleConfig, ConsoleOutputMode, CpusConfig, HotplugMethod, MemoryConfig, PayloadConfig,
-        RngConfig, VmConfig,
+        RngConfig,
     };
 
     fn create_dummy_vmm() -> Vmm {