nios2: Kconfig: remove some unused config options

We get these out of system.h instead. A clause in libc-hooks.c
for newlib added since we don't get RAM size from
CONFIG_SRAM_BASE_ADDRESS.

Change-Id: Ic35113395b951f625e8e29658afe19c525037964
Signed-off-by: Andrew Boie <andrew.p.boie@intel.com>