Bug 1703016 - Run android xpcshell in fewer test chunks; r=jmaher

Run android xpcshell in 2 test chunks instead of 4. Also remove custom max-run-time as it is not needed.

Differential Revision: https://phabricator.services.mozilla.com/D110804

taskcluster/ci/test/xpcshell.yml

@@ -54,7 +54,7 @@ xpcshell:
         by-test-platform:
             .*-ccov.*/.*: 6
             windows10-64-ccov-qr/opt: 6
-            android-em-7.*: 4
+            android-em-7.*: 2
             macosx1014-64(-shippable|-devedition|-asan)?(-qr)?/.*: 2
             linux1804-64(-qr)?/debug: 6
             .*-tsan/opt: 8
@@ -66,7 +66,6 @@ xpcshell:
             windows(7-32|10-64)(-shippable)?/opt: 5400
             .*-ccov.*/.*: 7200
             .*-tsan/opt: 7200
-            android-em-7.*: 5400
             default: 2700
     allow-software-gl-layers: false
     tier: