bq-picmt: move to unmaintained (MR 1912)

Right now the "bq-picmt" device port is quite confusing.
It's actually for the same device as "bq-paella", which is in community
and uses the mainline kernel, except that it uses the downstream kernel.

Having the downstream kernel packaged is useful for testing sometimes,
but otherwise the device package is completely unsupported.
The mainline port works much better. The downstream port should only
be used if you know what you are doing (e.g. because you want to test
if something is working on downstream but not mainline) and therefore
it should not show up in "pmbootstrap init" by default.

Move the device package to unmaintained to implement that.
Also, add an "# Unmaintained: ..." comment that will be displayed
in "pmbootstrap init" if the device is selected anyway.

device/testing/device-bq-picmt/APKBUILD → device/unmaintained/device-bq-picmt/APKBUILD

-# Maintainer: Jonathan Albrieux <jonathan.albrieux@gmail.com>
+# Unmaintained: Downstream port, only for testing. Use mainline port (bq-paella)!
 # Reference: <https://postmarketos.org/devicepkg>
 pkgname=device-bq-picmt
 pkgdesc="BQ Aquaris X5"

device/testing/linux-bq-picmt/APKBUILD → device/unmaintained/linux-bq-picmt/APKBUILD

-# Maintainer: Jonathan Albrieux <jonathan.albrieux@gmail.com>
+# Unmaintained: Downstream port, only for testing. Use mainline port (bq-paella)!
 # Reference: <https://postmarketos.org/vendorkernel>
 # Kernel config based on: arch/arm/configs/picmt_defconfig