Update mesh_system_heap_error_handler to use new error handler

[KariHaapalehto]

Update mesh_system_heap_error_handler to use new error codes and mbed

Description

Tested with K64F with EPS8266

Fixes: #6853

Pull request type

[X] Fix
[ ] Refactor
[ ] Target update
[ ] Feature
[ ] Breaking change

[cmonr]

/morph build

[mbed-ci]

Build : SUCCESS

Build number : 2785
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/7771/

Triggering tests

/morph test
/morph uvisor-test
/morph export-build
/morph mbed2-build

[mbed-ci]

Exporter Build : SUCCESS

Build number : 2416
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/exporter/7771/

[mbed-ci]

Test : SUCCESS

Build number : 2522
Test logs :http://mbed-os-logs.s3-website-us-west-1.amazonaws.com/?prefix=logs/7771/2522