The std::complex partial specializations have been unnecessary since
774c3d8647cc7012937cfc9d2d6dacc85b6cf8e9

Signed-off-by: Jonathan Wakely <jwakely@redhat.com>

libstdc++-v3/ChangeLog:

	* include/ext/type_traits.h (__promote_2, __promote_3)
	(__promote_4): Redfine as alias templates using __promoted_t.
	* include/std/complex (__promote_2): Remove partial
	specializations for std::complex.

Tested powerpc64le-linux. Committed to trunk.