Remove std::byte overloads from <bit>

Remove std::byte overloads from <bit>

The additional overloads for std::byte in <bit> were reviewed by LEWG
and considered undesirable, so this patch removes them.

Backport from mainline (partial)
2019-06-26  Jonathan Wakely  <jwakely@redhat.com>

	* include/std/bit (rotl(byte, unsigned), rotr(byte, unsigned))
	(countl_zero(byte), countl_one(byte), countr_zero(byte))
	(countr_one(byte), popcount(byte), ispow2(byte), ceil2(byte))
	(floor2(byte), log2p1(byte)): Remove.
	* testsuite/26_numerics/bit/bit.pow.two/ceil2.cc: Remove test for
	std::byte overload.
	* testsuite/26_numerics/bit/bit.pow.two/floor2.cc: Likewise.
	* testsuite/26_numerics/bit/bit.pow.two/ispow2.cc: Likewise.
	* testsuite/26_numerics/bit/bit.pow.two/log2p1.cc: Likewise.
	* testsuite/26_numerics/bit/bitops.count/countl_one.cc: Likewise.
	* testsuite/26_numerics/bit/bitops.count/countl_zero.cc: Likewise.
	* testsuite/26_numerics/bit/bitops.count/countr_one.cc: Likewise.
	* testsuite/26_numerics/bit/bitops.count/countr_zero.cc: Likewise.
	* testsuite/26_numerics/bit/bitops.count/popcount.cc: Likewise.
	* testsuite/26_numerics/bit/bitops.rot/rotl.cc: Likewise.
	* testsuite/26_numerics/bit/bitops.rot/rotr.cc: Likewise.

From-SVN: r273834