* with only one source bundle (per JEP-296), we can use src instead of
srcs, and avoid the need to cd in prePatch
* fetch sources from jdk10u instead of jdk10, to make it easier to
grab updates when they start coming.
* removed commented-out code that became irrelevant in the 8 -> 9
transition (*.pf files, infinality font rendering)
* create jdk10, jre10, and jre10_headless attributes in
all-packages.nix
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