Remove 2 superfluous use lines from ExtUtils::CBuilder.

use IO::File was added with the upgrade to 0.23 (commit c3fb68a339256eb3 in
April 2008), but the use of IO::File in the code was eliminated by the
upgrade to 0.2800 (commit 06e8058f27e4269b in Dec 2010), which replaced
the code in question with use of File::Temp. The latter refactoring also
added the use Data::Dumper; line, but did not add any code which uses
Data::Dumper.