Move usage of Runnable::run to TelephonyUtils

Using Runnable::run in com.android.internal.telephony from this
directory will conflict with any usages from frameworks/opt/telephony
since the compiles apparently scopes method references at the package
level. Move it to TelephonyUtils (which is in the .util sub-package) to
avoid the conflict.

Bug: 156779270
Test: build
Change-Id: I3471162eecde869aea66533de0355b3214859098