[sqlite] sqlite3rbu: void function returns value

[Ralf Junker]

Warning: sqlite3rbu.c 3528: void functions may not return a value in 
function rbuVfsDlClose.

http://www.sqlite.org/src/artifact/d37e1ca2d13e439c?ln=3526-3529

Looks like the return value is not needed.

Ralf