[BLE] HeartRateService/Heart Rate Measurement should not be Read

[Nodraak]

Description

• Type: Bug
• Priority: Minor
• Related file: https://github.com/ARMmbed/mbed-os/tree/master/features/FEATURE_BLE/ble/services/HeartRateService.h#L61

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According to the BLE spec (link found in HeartRateService.h), the Heart Rate Measurement characteristic of this service should be only Notify, and not Read.

[0xc0170]

cc @pan-