Remove DataSyncInterval variable from Config as not used anymore.

[sudiptob2]

DoD

1. Remove the variable from the code
2. remove env var declaration from config.yml(s)

Ref:

unicorn-history-server/internal/config/config.go

Lines 27 to 35 in e863911

	type UHSConfig struct {
	// Port specifies the port on which the Unicorn History Server listens for incoming requests.
	Port int
	// AssetsDir specifies the directory where the static assets are stored.
	AssetsDir string
	// DataSyncInterval specifies the interval at which the data is synced from the Yunikorn API.
	DataSyncInterval time.Duration
	// CORSConfig specifies the configuration for the CORS middleware.
	CORSConfig CORSConfig