Remove the usage of SystemProperties.set()

The usage of SystemProperties.set() in MockableSystemProperties
is either replaced by sysprop or removed. Thus, remove it to
suppport incoming ConnectivityService mainline.

Bug: 170917042
Test: m ; atest FrameworksNetTests
Change-Id: I99b3f200985c43e9338d828bd5b6bee323d61579
1 file changed