Remove unwanted (and unused anymore) NRF5_SDK13 BLE port

[nvlsianpu]

Description

Remove unwanted and unused anymore NRF5_SDK13 BLE port.
It was omited in #4245.

cc @pan-

[0xc0170]

retest uvisor

[AnotherButler]

@nvlsianpu Thanks for the PR.

Also, we're recommending all contributors follow Chris Beam’s seven rules of great commit messages to keep the commit history clear. To match this format, please delete the period from the end of your subject line. Thanks for your contributions.

[0xc0170]

retest uvisor

[0xc0170]

/morph test

[mbed-bot]

Result: NOT_BUILT

Your command has finished executing! Here's what you wrote!

/morph test

[0xc0170]

@bridadan CI restart? I noticed 5 jobs resulted the same as the one above - did not built

[bridadan]

@0xc0170 yeah go ahead, not sure what the happened there.

[0xc0170]

/morph test

[mbed-bot]

Result: SUCCESS

Your command has finished executing! Here's what you wrote!

/morph test

Output

mbed Build Number: 251

All builds and test passed!

[pan-]

test ble

{ 
    "targets": ["NRF51_DK", "NRF52_DK"],
    "toolchains": ["GCC_ARM", "ARM"]
}

[theotherjimmy]

@pan- where's the IAR testing?

[pan-]

@theotherjimmy Until Oulu CI is fixed, there will be no BLE testing with IAR on PR tests; but there is with nighties.
This PR is just about removing dead code, it shouldn't be an issue.