Remove duplicate link to 'custom VFSes' in README (#279)

Author: mtlynch

README.md

@@ -47,7 +47,7 @@ db.QueryRow(`SELECT sqlite_version()`).Scan(&version)
 - [nested transactions](https://sqlite.org/lang_savepoint.html)
 - [custom functions](https://sqlite.org/c3ref/create_function.html)
 - [virtual tables](https://sqlite.org/vtab.html)
-- [custom VFSes](https://sqlite.org/vfs.html)
+- [custom VFSes](vfs/README.md#custom-vfses)
 - [online backup](https://sqlite.org/backup.html)
 - [JSON support](https://sqlite.org/json1.html)
 - [math functions](https://sqlite.org/lang_mathfunc.html)
@@ -57,7 +57,6 @@ db.QueryRow(`SELECT sqlite_version()`).Scan(&version)
 - [statistics functions](https://pkg.go.dev/github.com/ncruces/go-sqlite3/ext/stats)
 - [encryption at rest](vfs/adiantum/README.md)
 - [many extensions](ext/README.md)
-- [custom VFSes](vfs/README.md#custom-vfses)
 - [and more…](embed/README.md)
 
 ### Caveats