devel/cmake-core: remove outdated FindOpenMP.cmake patch

This patch broke the build of any armv6/armv7 package that tried to
use OpenMP. It was once appropriate, but is now no longer correct
or needed.

PR: 270954
MFH: 2023Q2
Approved by: ports-secteam (fluffy), adridg
Tested by: portmgr (antoine, exp-run)