Remove unnecessary sync from FsBlobStore (#95412)

This confused me while looking into something unrelated.
There's no need to sync a createDirectories call like this,
the file system does that for us.
We do however in some cases create containers concurrently across
many threads which visbly blocks here.

Author: original-brownbear

server/src/main/java/org/elasticsearch/common/blobstore/fs/FsBlobStore.java

@@ -50,26 +50,22 @@ public int bufferSizeInBytes() {
 
     @Override
     public BlobContainer blobContainer(BlobPath path) {
-        try {
-            return new FsBlobContainer(this, path, buildAndCreate(path));
-        } catch (IOException ex) {
-            throw new ElasticsearchException("failed to create blob container", ex);
+        Path f = buildPath(path);
+        if (readOnly == false) {
+            try {
+                Files.createDirectories(f);
+            } catch (IOException ex) {
+                throw new ElasticsearchException("failed to create blob container", ex);
+            }
         }
+        return new FsBlobContainer(this, path, f);
     }
 
     @Override
     public void close() {
         // nothing to do here...
     }
 
-    private synchronized Path buildAndCreate(BlobPath path) throws IOException {
-        Path f = buildPath(path);
-        if (readOnly == false) {
-            Files.createDirectories(f);
-        }
-        return f;
-    }
-
     private Path buildPath(BlobPath path) {
         List<String> paths = path.parts();
         if (paths.isEmpty()) {