doc: Remove claim about large shared_buffers on Windows
Testing has shown that it is no longer correct.
From: Tsunakawa, Takayuki <tsunakawa.takay@jp.fujitsu.com>
Reviewed-by: amul sul <sulamul@gmail.com>
Discussion: http://www.postgresql.org/message-id/flat/
0A3221C70F24FB45833433255569204D1F5EE995@G01JPEXMBYT05/