Delete undeclared variable in guest-agent API class

The commit c7d93e7ce74c20a9c59ee0d2d542ed5b54d9c39c (not linked to
a gerrit review) introduced a local variable "timeout", used in a
 method of the API class

The review I9ad1b441eca855a4304454014ae746ec51bef8f3 deleted the
declaration of this variable but did not remove where it was used
in the class.

This patch removes the unused variable.

Closes-Bug: #1332333
Change-Id: Ie7aa66ceeca4efe63d91d60bcedb760ec181d443
Merge "Delete undeclared variable in guest-agent API class"