For one, intended warnings about pointers as function call arguments being
implicitly converted to bool are also covered (along with more) by
loplugin:implicitboolconversion.  For another, this code generates false
positives inside lambdas (where the check for CallExpr eventually always hits in
the PointerToBool::ignoreConversion recursion), see
762e90ff "vcl: loplugin:pointertobool."

Change-Id: I55eaa668c1b4a2c66a5a015b2414bf161f796f2a