Fix sync-point comment in Block destructor (#4380)

Summary:
This is a follow up to #4370. The earlier comment is not correct.

Thanks to ajkr for pointing this out.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/4380

Differential Revision: D9874667

Pulled By: sagar0

fbshipit-source-id: f4e092d86b29c715258210b770643d367e38caae

table/block.cc

@@ -763,8 +763,8 @@ BlockBasedTableOptions::DataBlockIndexType Block::IndexType() const {
 }
 
 Block::~Block() {
-  // This sync point can be re-enabled once the right order for global static
-  // initialization/destruction across compilation units is determined.
+  // This sync point can be re-enabled if RocksDB can control the
+  // initialization order of any/all static options created by the user.
   // TEST_SYNC_POINT("Block::~Block");
 }