fix(SDKManager): ignore enabled state for symbol management
fix(SDKManager): ignore enabled state for symbol management

Changes in the SDK Manager's inspector didn't lead to manage the
scripting define symbols. This fix changes that so neither the enabled
state of the SDK Manager script nor its game object influence the
management of the symbols for changes done in the inspector.

red-horizon/VRTK,thestonefox/SteamVR_Unity_Toolkit,virror/VRTK,adamjweaver/VRTK,thestonefox/VRTK,mattboy64/SteamVR_Unity_Toolkit,Innoactive/IA-unity-VR-toolkit-VRTK,gpvigano/VRTK,gomez-addams/SteamVR_Unity_Toolkit,TMaloteaux/SteamVR_Unity_Toolkit,gpvigano/SteamVR_Unity_Toolkit,Fulby/VRTK