Remove test

This test is not applicable anymore because it tests (and tested) the
wrong thing.

It was to check whether the function failed because the "imag" key
contained the wrong type, but this is not tested by that function. The
function only checks whether the "imag" key is present.

lib/core/libimagstore/src/store.rs

@@ -1148,14 +1148,6 @@ mod test {
         assert!(has_main_section(&Value::Table(map)).unwrap());
     }
 
-    #[test]
-    fn test_imag_invalid_section_type() {
-        let mut map = BTreeMap::new();
-        map.insert("imag".into(), Value::Boolean(false));
-
-        assert!(!has_main_section(&map));
-    }
-
     #[test]
     fn test_imag_abscent_main_section() {
         let mut map = BTreeMap::new();