libstdc++: Remove duplicate include header from ranges_algobase.h

libstdc++: Remove duplicate include header from ranges_algobase.h

The bits/stl_algobase.h header was added to bits/ranges_algobase.h
separately through two related commits:
r15-1106-g674d213ab91871
r15-1117-g0bb1db32ccf54a

The comment for the first time it is included in the file is also
incorrect (my error from that 2nd one) since it is really being included
for __memcmp, not __memcpy

This patch removes the duplicate header include.

libstdc++-v3/ChangeLog:

	* include/bits/ranges_algobase.h: Remove duplicate include of
	<bits/stl_algobase.h>.

Signed-off-by: Michael Levine <mlevine55@bloomberg.net>