I have long strugled with this problem.
The installer/unsnstaller accepts very few commandline options, and none to suppress a reboot.

I found this tip at community.microfucus.com:

Avoiding a reboot when silently uninstalling Silk Performer.
InstallAnywhere, the installer software, determines whether a restart is required during installation and uninstallation.  In silent mode the dialog prompt that asks for confirmation to allow the restart is not displayed and the machine restarts. 

The restart can be disabled by adding the following flag to the silent.properties file:
#disable restart