Revert "Enable sext.w removal for riscv targets"

This reverts commit bce5507c02.

The update of LLVM to clang-r498229 resolved the error with sext.w as
resolved in D143594.

Bug: 275574215
Test: Verified boot of riscv64 phone target.
Change-Id: Ie31b7db03004c5aafb6067713ef5f819e0706b64

cc/config/riscv64_device.go

@@ -26,9 +26,6 @@ var (
 		// Help catch common 32/64-bit errors.
 		"-Werror=implicit-function-declaration",
 		"-fno-emulated-tls",
-		// A temporary fix for SExtWRemoval miscompilation bug.
-		"-mllvm",
-		"-riscv-disable-sextw-removal=true",
 		"-march=rv64gc_zba_zbb_zbs",
 	}