Sorry to necro this thread but it's the third Google result for "Healbot Holy Power."
Go to the Bar Option part of Healbot. In the version I'm using it's a subgroup called Bars underneath Frames. This menu will have options to change "Texture," "No. columns," "Height," "Width," "Row Spacer," "Col spacer," "Aggro bar size," and "Power bar size." Underneath the "Power Bar size" in my version of Healbot, there was a small radio button titled "Show power counter." Click that off to turn off Holy Power in the Healbot frames.