merge_tools: move "ui.diff-instructions" to CLI and config/misc.toml

There are no users of this option in jj-lib. Let's simplify it.

cli/src/config/misc.toml

@@ -5,6 +5,7 @@
 tree-level-conflicts = true
 
 [ui]
+diff-instructions = true
 paginate = "auto"
 pager = { command = ["less", "-FRX"], env = { LESSCHARSET = "utf-8" } }
 log-word-wrap = false

cli/src/merge_tools/mod.rs

@@ -182,7 +182,7 @@ impl DiffEditor {
         Ok(DiffEditor {
             tool,
             base_ignores,
-            use_instructions: settings.diff_instructions(),
+            use_instructions: settings.config().get_bool("ui.diff-instructions")?,
         })
     }
 

lib/src/settings.rs

@@ -228,10 +228,6 @@ impl UserSettings {
             .unwrap_or(false)
     }
 
-    pub fn diff_instructions(&self) -> bool {
-        self.config.get_bool("ui.diff-instructions").unwrap_or(true)
-    }
-
     pub fn config(&self) -> &config::Config {
         &self.config
     }