drivers/net: delete Racal Interlan ISA ni52 (i825xx) driver

Like the other drivers that were in the ISA i825xx family, the ni52
was rather rare, not widely used, and hence perhaps not as reliable
as the more mainstream ISA drivers that were heavily used.  Given
that, it is chosen for retirement at this time as well.

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>