runtime-rs: Remove unused config

`gdb` is only activated by a feature `guest_debug` that doesn't
exist, so remove this.

Signed-off-by: stevenhorsman <steven@uk.ibm.com>

src/runtime-rs/crates/hypervisor/ch-config/src/lib.rs

@@ -446,8 +446,6 @@ pub struct VmConfig {
     pub numa: Option<Vec<NumaConfig>>,
     #[serde(default)]
     pub watchdog: bool,
-    #[cfg(feature = "guest_debug")]
-    pub gdb: bool,
     #[serde(skip_serializing_if = "Option::is_none")]
     pub platform: Option<PlatformConfig>,
 }