Remove support for using ninja flash/debug on hardware without installing west with pip

[carlescufi]

As described in the documentation, today it is still supported to be able to execute the flash and debug build targets when west is not installed in the system with pip, via the use of the WEST_DIR optional variable. This added complexity is not deemed worthwhile, and so we should remove the support for it.

[marc-hb]

I understand the desire to remove WEST_DIR and simplify but why does pip matter? As long as west can be found in the PATH then it's enough and OK, correct? I hope it does not matter where west came from.

[zephyrbot]

Hi @tejlmand,

This issue, marked as an Enhancement, was opened a while ago and did not get any traction. Please confirm the issue is correctly assigned and re-assign it otherwise.

Please take a moment to review if the issue is still relevant to the project. If it is, please provide feedback and direction on how to move forward. If it is not, has already been addressed, is a duplicate, or is no longer relevant, please close it with a short comment explaining the reason.

@carlescufi you are also encouraged to help moving this issue forward by providing additional information and confirming this request/issue is still relevant to you.

Thanks!