fix: remove unnecessary function cache (#1358)

This is just a bit of code cleanup; I think this cache logic is excessive

src/routes/_utils/isMobile.js

@@ -1,11 +0,0 @@
-// Rough guess at whether this is a "mobile" device or not, for the purposes
-// of "device class" estimations
-
-let cached
-
-export function isMobile () {
-  if (typeof cached === 'undefined') {
-    cached = !!(process.browser && navigator.userAgent.match(/(iPhone|iPod|iPad|Android)/))
-  }
-  return cached
-}

src/routes/_utils/runMediumPriorityTask.js

@@ -1,6 +1,9 @@
 import { scheduleIdleTask } from './scheduleIdleTask'
 import { store } from '../_store/store'
-import { isMobile } from './isMobile'
+
+// Rough guess at whether this is a "mobile" device or not, for the purposes
+// of "device class" estimations
+const IS_MOBILE = process.browser && navigator.userAgent.match(/(?:iPhone|iPod|iPad|Android)/)
 
 // Run a task that doesn't need to be processed immediately, but should
 // probably be delayed if we're on a mobile device. Also run it sooner
@@ -8,7 +11,7 @@ import { isMobile } from './isMobile'
 export function runMediumPriorityTask (fn) {
   if (store.get().pageVisibilityHidden) {
     fn()
-  } else if (isMobile()) {
+  } else if (IS_MOBILE) {
     scheduleIdleTask(fn)
   } else {
     requestAnimationFrame(fn)