Always sync-safekeepers in neon_local on compute start.

Instead of checking neon.safekeepers GUC value in existing pg node data dir,
just always run sync-safekeepers when safekeepers are configured. Without this
change, creation of new compute didn't run it. That's ok for new
timeline/branch (it doesn't return anything useful anyway, and LSN is known by
pageserver), but restart of compute for existing timeline bore the risk of
getting basebackup not on the latest LSN, i.e. basically broken -- it might not
have prev_lsn, and even if it had, walproposer would complain anyway.

fixes https://github.com/neondatabase/neon/issues/2963

control_plane/src/compute.rs

@@ -90,7 +90,6 @@ impl ComputeControlPlane {
             timeline_id,
             lsn,
             tenant_id,
-            uses_wal_proposer: false,
             pg_version,
         });
 
@@ -115,7 +114,6 @@ pub struct PostgresNode {
     pub timeline_id: TimelineId,
     pub lsn: Option<Lsn>, // if it's a read-only node. None for primary
     pub tenant_id: TenantId,
-    uses_wal_proposer: bool,
     pg_version: u32,
 }
 
@@ -149,7 +147,6 @@ impl PostgresNode {
         let port: u16 = conf.parse_field("port", &context)?;
         let timeline_id: TimelineId = conf.parse_field("neon.timeline_id", &context)?;
         let tenant_id: TenantId = conf.parse_field("neon.tenant_id", &context)?;
-        let uses_wal_proposer = conf.get("neon.safekeepers").is_some();
 
         // Read postgres version from PG_VERSION file to determine which postgres version binary to use.
         // If it doesn't exist, assume broken data directory and use default pg version.
@@ -172,7 +169,6 @@ impl PostgresNode {
             timeline_id,
             lsn: recovery_target_lsn,
             tenant_id,
-            uses_wal_proposer,
             pg_version,
         })
     }
@@ -364,7 +360,7 @@ impl PostgresNode {
     fn load_basebackup(&self, auth_token: &Option<String>) -> Result<()> {
         let backup_lsn = if let Some(lsn) = self.lsn {
             Some(lsn)
-        } else if self.uses_wal_proposer {
+        } else if !self.env.safekeepers.is_empty() {
             // LSN 0 means that it is bootstrap and we need to download just
             // latest data from the pageserver. That is a bit clumsy but whole bootstrap
             // procedure evolves quite actively right now, so let's think about it again