Time Zones: Fix relative time when using UTC timezone (#85637)

add UTC case to e2e test + let UTC pass through to moment.tz

e2e/dashboards-suite/dashboard-time-zone.spec.ts

@@ -112,6 +112,41 @@ describe('Dashboard time zone support', () => {
     // Need to wait for 2 calls as there's 2 panels
     cy.wait(['@dataQuery', '@dataQuery']);
 
+    e2e.components.Panels.Panel.title('Panel with relative time override')
+      .should('be.visible')
+      .within(() => {
+        cy.contains('[role="row"]', '00:00:00').should('be.visible');
+      });
+
+    e2e.components.Panels.Panel.title('Panel in timezone')
+      .should('be.visible')
+      .within(() => {
+        cy.contains('[role="row"]', '00:00:00').should('be.visible');
+      });
+
+    // Test UTC timezone
+    e2e.flows.setTimeRange({
+      from: 'now-6h',
+      to: 'now',
+      zone: 'Coordinated Universal Time',
+    });
+    // Need to wait for 2 calls as there's 2 panels
+    cy.wait(['@dataQuery', '@dataQuery']);
+
+    e2e.components.Panels.Panel.title('Panel with relative time override')
+      .should('be.visible')
+      .within(() => {
+        cy.contains('[role="row"]', '00:00:00').should('be.visible');
+      });
+
+    // Today so far, still in UTC timezone
+    e2e.flows.setTimeRange({
+      from: 'now/d',
+      to: 'now',
+    });
+    // Need to wait for 2 calls as there's 2 panels
+    cy.wait(['@dataQuery', '@dataQuery']);
+
     e2e.components.Panels.Panel.title('Panel with relative time override')
       .should('be.visible')
       .within(() => {

packages/grafana-data/src/datetime/moment_wrapper.ts

@@ -126,10 +126,6 @@ export const dateTimeForTimeZone = (
   input?: DateTimeInput,
   formatInput?: FormatInput
 ): DateTime => {
-  if (timezone === 'utc') {
-    return toUtc(input, formatInput);
-  }
-
   if (timezone && timezone !== 'browser') {
     let result: moment.Moment;