refactor: Move ts_to_timestamp fn into the only file it's used in

server/src/db/system_tables.rs

@@ -14,7 +14,6 @@ use arrow::{
     error::Result,
     record_batch::RecordBatch,
 };
-use chrono::{DateTime, Utc};
 use datafusion::{
     catalog::schema::SchemaProvider,
     datasource::{datasource::Statistics, TableProvider},
@@ -153,11 +152,6 @@ where
     }
 }
 
-// TODO: Use a custom proc macro or serde to reduce the boilerplate
-fn time_to_ts(time: Option<DateTime<Utc>>) -> Option<i64> {
-    time.map(|ts| ts.timestamp_nanos())
-}
-
 /// Creates a DataFusion ExecutionPlan node that scans a single batch
 /// of records.
 fn scan_batch(

server/src/db/system_tables/chunks.rs

@@ -1,13 +1,11 @@
-use crate::db::{
-    catalog::Catalog,
-    system_tables::{time_to_ts, IoxSystemTable},
-};
+use crate::db::{catalog::Catalog, system_tables::IoxSystemTable};
 use arrow::{
     array::{StringArray, TimestampNanosecondArray, UInt32Array, UInt64Array},
     datatypes::{DataType, Field, Schema, SchemaRef, TimeUnit},
     error::Result,
     record_batch::RecordBatch,
 };
+use chrono::{DateTime, Utc};
 use data_types::{chunk_metadata::ChunkSummary, error::ErrorLogger};
 use std::sync::Arc;
 
@@ -56,6 +54,11 @@ fn chunk_summaries_schema() -> SchemaRef {
     ]))
 }
 
+// TODO: Use a custom proc macro or serde to reduce the boilerplate
+fn time_to_ts(time: Option<DateTime<Utc>>) -> Option<i64> {
+    time.map(|ts| ts.timestamp_nanos())
+}
+
 fn from_chunk_summaries(schema: SchemaRef, chunks: Vec<ChunkSummary>) -> Result<RecordBatch> {
     let id = chunks.iter().map(|c| Some(c.id)).collect::<UInt32Array>();
     let partition_key = chunks