Allow linear backoff policy for UI jobs.

UI jobs were initially required to have an exponential backoff
as a way to reduce keep-alive abuse. Now that UI jobs have a
cumulative execution limit, there's little reason to disallow a
linear backoff policy.

Bug: 261999509
Test: atest CtsJobSchedulerTestCases:JobInfoTest
Change-Id: I88300b0fb64b1ca34123d3e16eb8e1fa81c586d6

apex/jobscheduler/framework/java/android/app/job/JobInfo.java

@@ -2344,11 +2344,7 @@ public class JobInfo implements Parcelable {
             // UIDTs
             if (networkRequest == null) {
                 throw new IllegalArgumentException(
-                        "A user-initaited data transfer job must specify a valid network type");
-            }
-            if (backoffPolicy == BACKOFF_POLICY_LINEAR) {
-                throw new IllegalArgumentException(
-                        "A user-initiated data transfer job cannot have a linear backoff policy.");
+                        "A user-initiated data transfer job must specify a valid network type");
             }
         }
     }