This reverts the Flex-related parts of commit
rBef268c78933079137288e326704431432adf9ad9, as those caused a build
error on CentOS 7 (which is used for the precompiled Linux libraries).
CentOS 7 only has Automake 1.13, whereas after this commit version 1.15
seems to be required.
Since in its patch description (D15319) it's mentioned that this
"probably doesn't warrant changing", and it's actually blocking the
build of the precompiled libraries for Blender 3.3 now, I'll revert the
Flex-related part of the commit.
Sybren A. Stüvel
e4a779264c