Delete vestigial last_run.uuid file

This file gets written with a random UUID every time you download the
schema. The line that writes it was added in #119 along with a special
`cargo:rerun-if-changed` command to control if Cargo is rerun. However,
that check was removed in #1166. (And then this entire update procedure
was moved from `build.rs` to an explicitly-run `xtask` command in #1424.)

So it seems like this file is completely vestigial at this point and
doesn't need to be updated when you update the schema.

xtask/src/commands/prep/main_schema.rs

@@ -17,8 +17,6 @@ const SCHEMA_DIR: &str = "./crates/rover-client/.schema";
 pub async fn update() -> Result<()> {
     let schema_dir = Utf8PathBuf::from(SCHEMA_DIR);
     Fs::create_dir_all(&schema_dir)?;
-    let last_run_uuid = Uuid::new_v4().to_string();
-    Fs::write_file(schema_dir.join("last_run.uuid"), last_run_uuid)?;
 
     let hash_path = schema_dir.join("hash.id");