foamJob calls missing script foamExec (OF-v1812 and -v1906)

bin/foamJob calls the script foamExec, but foamExec does not exist in the OpenFOAM-v1812 or -v1906 distributions.

Issue report 1309, "foamExec file is missing," was closed without a change, but did not address the effect on foamJob from the missing foamExec. OpenFOAM-plus#1309 (closed)

foamExec is missing only from OF-v1812 and -1906. OF-7 still contains foamExec.

Thanks.

## Reattaching the author to the issue ticket: @gcEngineer ##