move grub-pc specific code to actual grub-pc script

reintroduces the commit that was dropped from a different MR due to my having forgotten to add an ISO based condition around it in the new location, with this now fixed of course.

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the grub-pc image creation code has no business being in binary_iso, it should be in binary_grub-pc.

it should be noted that the binary_iso script did not even have the necessary package check for grub-mkimage, while binary_grub-pc did have it, pointlessly.

Gbp-Dch: Short

added 4 commits

• 1530be72...49794f11 - 3 commits from branch live-team:master
• bf637627 - move grub-pc specific code to actual grub-pc script

Compare with previous version

merged