intel_s1000_crb: kconfig: Remove unused I2C_0_DEFAULT_CFG symbol

Unused since commit 7e96ca5d ("i2c: Remove non DTS Kconfig params").

intel_s1000_crb probably isn't getting tested in CI, because Kconfiglib
generated a warning for the symbol no longer being given a type, which
would be turned into an error.

Signed-off-by: Ulf Magnusson <Ulf.Magnusson@nordicsemi.no>