glibc: drop redundant arch depends

These are already in toolchain/toolchain-buildroot/Config.in and since
package/glibc/Config.in is filtered by BR2_TOOLCHAIN_USES_GLIBC there's
no need to duplicate this.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Acked-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>