i965/vec4: Delete some dead code in visit(ir_expression *).

i965/vec4: Delete some dead code in visit(ir_expression *).

Nothing uses the vector_elements temporary variable.

Setting this->result.file is dead because we overwrite this->result a
few lines later.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>