refactor(http2): store bdp sampler in Body H2 variant

src/proto/h2/bdp.rs

@@ -30,7 +30,7 @@ type WindowSize = u32;
 /// Any higher than this likely will be hitting the TCP flow control.
 const BDP_LIMIT: usize = 1024 * 1024 * 16;
 
-pub(crate) fn disabled() -> Sampler {
+pub(super) fn disabled() -> Sampler {
     Sampler {
         shared: Weak::new(),
     }
@@ -105,10 +105,6 @@ impl Sampler {
 
         inner.bytes += bytes;
     }
-
-    pub(crate) fn is_enabled(&self) -> bool {
-        self.shared.strong_count() > 0
-    }
 }
 
 impl Estimator {