options, '-Wc++[...]-extensions': Remove undefined one-argument 'LangEnabledBy' optio...

options, '-Wc++[...]-extensions': Remove undefined one-argument 'LangEnabledBy' option properties

A one-argument form of the 'LangEnabledBy' option property isn't defined,
and effectively appears to be a no-op.  Removing these only changes
'build-gcc/gcc/optionlist' accordingly, but no other generated files.

Clean-up for commit ee336ecb2a7161bc28f6c5343d97870a8d15e177
"c++: Add new warning options for C++ language mismatches".

	gcc/c-family/
	* c.opt (Wc++11-extensions, Wc++14-extensions, Wc++17-extensions)
	(Wc++20-extensions, Wc++23-extensions): Remove 'LangEnabledBy'
	option properties.