Remove file I/O from tests that don't need it (#11182)

# Description

This PR implements modifications to command tests that write unnecessary
json and csv to disk then load it with open, by using nuon literals
instead.

- Fixes #7189



# User-Facing Changes
None

# Tests + Formatting
This only affects existing tests, which still pass.

crates/nu-command/tests/commands/uniq_by.rs

@@ -1,32 +1,24 @@
-use nu_test_support::fs::Stub::FileWithContentToBeTrimmed;
-use nu_test_support::playground::Playground;
 use nu_test_support::{nu, pipeline};
 
 #[test]
 fn removes_duplicate_rows() {
-    Playground::setup("uniq_test_1", |dirs, sandbox| {
-        sandbox.with_files(vec![FileWithContentToBeTrimmed(
-            "los_tres_caballeros.csv",
-            r#"
-                first_name,last_name,rusty_at,type
-                Andrés,Robalino,10/11/2013,A
-                Afonso,Turner,10/12/2013,B
-                Yehuda,Katz,10/11/2013,A
-                JT,Turner,11/12/2011,O
-            "#,
-        )]);
+    let sample = r#"
+                    [[first_name , last_name, rusty_at, type];
+                     [Andrés     , Robalino, "10/11/2013", A],
+                     [Afonso     , Turner, "10/12/2013", B],
+                     [Yehuda     , Katz, "10/11/2013", A],
+                     [JT         , Turner, "11/12/2011", O]]
+            "#;
 
-        let actual = nu!(
-            cwd: dirs.test(), pipeline(
-            "
-                open los_tres_caballeros.csv
+    let actual = nu!(pipeline(&format!(
+        "
+                {sample}
                 | uniq-by last_name
                 | length
             "
-        ));
+    )));
 
-        assert_eq!(actual.out, "3");
-    })
+    assert_eq!(actual.out, "3");
 }
 
 #[test]