collab: Don't use a separate product for Zed Pro trials (#28986)

This PR removes the separate product used for the Zed Pro trials, in
favor of using Stripe's trial functionality.

Release Notes:

- N/A

crates/collab/src/lib.rs

@@ -207,13 +207,6 @@ impl Config {
         Self::parse_stripe_price_id("Zed Pro", self.stripe_zed_pro_price_id.as_deref())
     }
 
-    pub fn zed_pro_trial_price_id(&self) -> anyhow::Result<stripe::PriceId> {
-        Self::parse_stripe_price_id(
-            "Zed Pro Trial",
-            self.stripe_zed_pro_trial_price_id.as_deref(),
-        )
-    }
-
     pub fn zed_free_price_id(&self) -> anyhow::Result<stripe::PriceId> {
         Self::parse_stripe_price_id("Zed Free", self.stripe_zed_pro_price_id.as_deref())
     }