Supports mix of wasm and go funcs in the same module (#707)

This removes the constraint of a module being exclusively wasm or host
functions. Later pull requests can optimize special imports to be
implemented in wasm, particularly useful for disabled logging callbacks.

Signed-off-by: Adrian Cole <adrian@tetrate.io>

internal/wasm/counts.go

@@ -79,8 +79,6 @@ func (m *Module) SectionElementCount(sectionID SectionID) uint32 { // element as
 		return uint32(len(m.CodeSection))
 	case SectionIDData:
 		return uint32(len(m.DataSection))
-	case SectionIDHostFunction:
-		return uint32(len(m.HostFunctionSection))
 	default:
 		panic(fmt.Errorf("BUG: unknown section: %d", sectionID))
 	}