Remove getBitfieldCount method

Remove the getBitfieldCount method and use the C++20 feature
`std::popcount` to get the number of bits of 1.

Signed-off-by: George Liu <liuxiwei@inspur.com>
Change-Id: I71a5c1a9e10f508ce58a01ec8dc17ed5d96ed8a5
diff --git a/libpldmresponder/platform.cpp b/libpldmresponder/platform.cpp
index 893cc83..779a0cd 100644
--- a/libpldmresponder/platform.cpp
+++ b/libpldmresponder/platform.cpp
@@ -615,7 +615,7 @@
     }
 
     // 0x01 to 0x08
-    uint8_t sensorRearmCount = getBitfieldCount(sensorRearm);
+    uint8_t sensorRearmCount = std::popcount(sensorRearm.byte);
     std::vector<get_sensor_state_field> stateField(sensorRearmCount);
     uint8_t comSensorCnt{};
     const pldm::utils::DBusHandler dBusIntf;