StmtOpenMP.h: Fix bogus \param(s). [-Wdocumentation]

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@186664 91177308-0d34-0410-b5e6-96231b3b80d8
StmtOpenMP.h: Prune a stray \param in the comment of OMPExecutableDirective(). [-Wdocumentation]

-  /// \param Clauses A list of clauses.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@186665 91177308-0d34-0410-b5e6-96231b3b80d8