Revert "OpenMP 5.0 metadirective"

This reverts commit c7d7b98e5263472f05b2f3cb767b5d16e1349e9a.

GitOrigin-RevId: 7efb825382c0a8372597aaf75a319fa379573fd4
diff --git a/lib/Semantics/check-omp-structure.cpp b/lib/Semantics/check-omp-structure.cpp
index 2c1b291..3b58f97 100644
--- a/lib/Semantics/check-omp-structure.cpp
+++ b/lib/Semantics/check-omp-structure.cpp
@@ -1391,7 +1391,6 @@
 CHECK_SIMPLE_CLAUSE(Novariants, OMPC_novariants)
 CHECK_SIMPLE_CLAUSE(Nocontext, OMPC_nocontext)
 CHECK_SIMPLE_CLAUSE(Filter, OMPC_filter)
-CHECK_SIMPLE_CLAUSE(When, OMPC_when)
 
 CHECK_REQ_SCALAR_INT_CLAUSE(Grainsize, OMPC_grainsize)
 CHECK_REQ_SCALAR_INT_CLAUSE(NumTasks, OMPC_num_tasks)