tree-wide: Use cap-std-ext is_mountpoint() API

I moved it there a while ago, now we can drop the copy of it
here.

Signed-off-by: Colin Walters <[email protected]>

lib/src/install.rs

@@ -1711,7 +1711,7 @@ pub(crate) async fn install_to_filesystem(
 
         tracing::debug!("Root filesystem: {root_path}");
 
-        if let Some(false) = ostree_ext::mountutil::is_mountpoint(&rootfs_fd, ".")? {
+        if let Some(false) = rootfs_fd.is_mountpoint(".")? {
             anyhow::bail!("Not a mountpoint: {root_path}");
         }
         rootfs_fd

ostree-ext/src/commit.rs

@@ -3,7 +3,6 @@
 //! <https://github.com/ostreedev/ostree-rs-ext/issues/159>
 
 use crate::container_utils::require_ostree_container;
-use crate::mountutil::is_mountpoint;
 use anyhow::Context;
 use anyhow::Result;
 use cap_std::fs::Dir;
@@ -60,7 +59,7 @@ fn clean_subdir(root: &Dir, rootdev: u64) -> Result<()> {
         }
         // Also ignore bind mounts, if we have a new enough kernel with statx()
         // that will tell us.
-        if is_mountpoint(root, &path)?.unwrap_or_default() {
+        if root.is_mountpoint(&path)?.unwrap_or_default() {
             tracing::trace!("Skipping mount point {path:?}");
             continue;
         }

ostree-ext/src/lib.rs

@@ -39,7 +39,6 @@ pub mod diff;
 pub mod ima;
 pub mod keyfileext;
 pub(crate) mod logging;
-pub mod mountutil;
 pub mod ostree_prepareroot;
 pub mod refescape;
 #[doc(hidden)]