bitbake: Remove source directory variable in Whinlatter

[robwoolley]

Styhead requires that S = "${WORKDIR}" be replaced with S = "${UNPACKDIR}", however S = "${WORKDIR}/git" is still supported.

Whinlatter no longer supports setting S = "${WORKDIR}/git".

See the Yocto Project release notes for details.

[robwoolley]

Styhead

https://docs.yoctoproject.org/next/migration-guides/migration-5.1.html#workdir-changes
S = "${WORKDIR}" becomes S = "${UNPACKDIR}"

Note: "S = "${WORKDIR}/git" and also deeper paths continue to work as expected without changes."

Whinlatter

https://docs.yoctoproject.org/next/migration-guides/migration-5.3.html#workdir-changes

"S = ${WORKDIR}/something no longer supported"

" S setting in recipes can and should be removed."

when "git" as the source checkout location is hardcoded "in SRC_URI, replace with BB_GIT_DEFAULT_DESTSUFFIX, otherwise replace with BP."

How to make those adjustments without tedious manual editing
https://docs.yoctoproject.org/next/migration-guides/migration-5.3.html#how-to-make-those-adjustments-without-tedious-manual-editing