Don't generate useless GRAPHVIZ_VERSION file in macOS CMake build CI job
Pertaining to !2205 (comment 699666626), this is an addendum to !2205 (merged).
The Graphviz version is generated internally to a variable in the CMake build job and the downstream test job generates the GRAPHVIZ_VERSION file itself since commit fea17b6a.
This MR moves the generation of the GRAPHVIZ_VERSION file from the macOS build template to the macOS autotools build job and also does another minor related cleanup.