Apply the change from commit 57a78b55 (VS: Fix support for '/guard:cf'
linker flag, 2018-11-21) to the v142 flag table.

Although `$(VCTargetsPath)/1033/link.xml` contains an entry for
`LinkControlFlowGuard`, it does not work when used in a `.vcxproj` file
(at least as of v140 and v141).  Drop our link flag table entries for
these toolsets so that the flag will be passed via `AdditionalOptions`.