rust: remove !COMPILE_TEST gate

Now that we have `RUST_IS_AVAILABLE` with more checks, we can "safely"
remove `!COMPILE_TEST`.

Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Author: ojeda

init/Kconfig

@@ -2060,7 +2060,6 @@ config RUST
 	bool "Rust support"
 	depends on RUST_IS_AVAILABLE
 	depends on ARM64 || CPU_32v6 || CPU_32v6K || (PPC64 && CPU_LITTLE_ENDIAN) || X86_64 || RISCV
-	depends on !COMPILE_TEST
 	depends on !MODVERSIONS
 	depends on !GCC_PLUGIN_RANDSTRUCT
 	default n