pgsql: Remove reference to default wal_buffers being 8

Remove reference to default wal_buffers being 8

This hasn't been true since 9.1, when the default was changed to -1.
Remove the reference completely, keeping the discussion of the parameter
and it's shared memory effects on the config page.

Branch
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REL9_1_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/119027ec8b8d02c8d70e4916df1b41cde78f674d

Modified Files
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doc/src/sgml/wal.sgml |    4 +---
1 files changed, 1 insertions(+), 3 deletions(-)