Move events stubs to events/tests/UNITTESTS

[rajkan01]

Description of defect

To move events stubs to events/tests/UNITTESTS directory so the stubs live with the associated component

Target(s) affected by this defect ?

N/A

Toolchain(s) (name and version) displaying this defect ?

N/A

What version of Mbed-os are you using (tag or sha) ?

Latest

What version(s) of tools are you using. List all that apply (E.g. mbed-cli)

N/A

How is this defect reproduced ?

N/A

[mbedmain]

@rajkan01 thank you for raising this issue.Please take a look at the following comments:

Could you add some more detail to the description? A good description should be at least 25 words.

NOTE: If there are fields which are not applicable then please just add 'n/a' or 'None'. This indicates to us that at least all the fields have been considered.
Please update the issue header with the missing information.

[LDong-Arm]

Reopening this issue - the PR isn't merged yet.
Okay, it happened because two PRs were previously linked to this issue, and one of them was merged.