[sdk] Simplify dispose code in SelfDiagnostics (#6072)

Co-authored-by: Mikel Blanchard <mblanchard@macrosssoftware.com>

src/OpenTelemetry/Internal/SelfDiagnostics.cs

@@ -39,17 +39,6 @@ public static void EnsureInitialized()
     }
 
     /// <inheritdoc/>
-    public void Dispose()
-    {
-        this.Dispose(true);
-        GC.SuppressFinalize(this);
-    }
-
-    private void Dispose(bool disposing)
-    {
-        if (disposing)
-        {
-            this.configRefresher.Dispose();
-        }
-    }
+    public void Dispose() =>
+        this.configRefresher.Dispose();
 }