fix(tvix/eval): remove overlapping instances

I broke the build.

I didn't understand that before hitting "submit" you need to re-test
your changes on latest HEAD (and that CI doesn't do that for you); I
failed to re-test cl/6912 following the merge of cl/6907.

This commit fixes the build by removing the overlapping instances.

Change-Id: I2a720d2c60cc7103b350f78102a8998f93bac828
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6965
Tested-by: BuildkiteCI
Autosubmit: Adam Joseph <adam@westernsemico.com>
Reviewed-by: tazjin <tazjin@tvl.su>

tvix/eval/src/value/mod.rs

@@ -381,18 +381,6 @@ impl From<i64> for Value {
     }
 }
 
-impl From<&str> for Value {
-    fn from(val: &str) -> Self {
-        Self::String(val.into())
-    }
-}
-
-impl From<String> for Value {
-    fn from(val: String) -> Self {
-        Self::String(val.into())
-    }
-}
-
 impl From<PathBuf> for Value {
     fn from(path: PathBuf) -> Self {
         Self::Path(path)