Revert "arch: riscv: Enable builds without the multithreading"

This reverts commit f0b458a6192c33cbd7a88199c0691acfc80dc1ff.

This is a pointless change that simply increases footprint.
Existing code already supports compilation without multithreading.

Signed-off-by: Nicolas Pitre <npitre@baylibre.com>
2 files changed