Revert "Use SPEED_OPTIMIZATIONS on riscv for GCC 14.3"

This reverts commit 0a8f9a3.

I haven't been able to reproduce this issue again; let's go back to
using -Os and see if we can make it happen again someday.

Author: keith-packard

Kconfig.zephyr

@@ -491,8 +491,6 @@ choice COMPILER_OPTIMIZATIONS
 	prompt "Optimization level"
 	default NO_OPTIMIZATIONS    if COVERAGE
 	default DEBUG_OPTIMIZATIONS if DEBUG
-	# gcc 14.3 -Os is broken on riscv. This setting should be in the SDK, it's here for testing
-	default SPEED_OPTIMIZATIONS if "$(TOOLCHAIN_VARIANT_COMPILER)" = "gnu" && RISCV
 	default SIZE_OPTIMIZATIONS_AGGRESSIVE if "$(TOOLCHAIN_VARIANT_COMPILER)" = "llvm"
 	default SIZE_OPTIMIZATIONS
 	help