revert: let project beads config control sync-branch

The sync-branch setting is up to the project's .beads/config.yaml,
not something Gas Town should force. Projects can use bd doctor --fix
to configure sync-branch if they want multi-clone coordination.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/cmd/doctor.go

@@ -55,7 +55,6 @@ func runDoctor(cmd *cobra.Command, args []string) error {
 	// Register built-in checks
 	d.Register(doctor.NewDaemonCheck())
 	d.Register(doctor.NewBeadsDatabaseCheck())
-	d.Register(doctor.NewBeadsSyncBranchCheck())
 
 	// Run checks
 	var report *doctor.Report