cleanup: feature "man-pages" > "separate-binaries"

Rename some leftover (feature = "man-pages") to "separate-binaries"
which is more descriptive. This is still an un-implemented feature, but
it could be revived in the future for better user experience.

git-branchless-init/src/lib.rs

@@ -311,7 +311,7 @@ fn uninstall_hooks(effects: &Effects, git_run_info: &GitRunInfo, repo: &Repo) ->
 /// subcommand is included in the `man` invocation, so it can show more specific
 /// help.
 fn should_use_wrapped_command_alias() -> bool {
-    cfg!(feature = "man-pages")
+    cfg!(feature = "separate-binaries") // unimplemented
 }
 
 #[instrument]
@@ -694,7 +694,7 @@ contents 3
 
     #[test]
     fn test_all_alias_binaries_exist() {
-        let all_alias_binaries_installed = cfg!(feature = "man-pages");
+        let all_alias_binaries_installed = cfg!(feature = "separate-binaries"); // unimplemented
         if !all_alias_binaries_installed {
             return;
         }

git-branchless/tests/test_init.rs

@@ -363,7 +363,7 @@ fn test_init_uninstall() -> eyre::Result<()> {
     Ok(())
 }
 
-#[cfg(feature = "man-pages")]
+#[cfg(feature = "separate-binaries")] // unimplemented
 #[test]
 fn test_man_viewer_installed() -> eyre::Result<()> {
     use std::collections::HashMap;