[3.2] disable appbase's automatic version discovery via git

[ClaytonCalabrese]

Once upon a time in an eosio version long ago, the sole mechanism to populate the version displayed by, say, nodeos --version was via appbase discovering the version by git describe. At some point we changed this up a bit and the bottom line is that libraries/version is the only location that probes git for creating a string ultimately baked in to the build.

This makes the git describe in appbase a complete waste as its output is never included in to final executables. Since this git describe is run literally every time performing a make, seemed worth the trouble to disable it.

Needs eosnetworkfoundation/mandel-appbase#9

Resolves #442