[iOS]Updated "shard size" to "swarming tasks" for EG tests.

Depend on cl http://crrev/c/1954209 that will change
`shard size` logic, since this cl it will be number of swarming tasks,
not number of test classes per swarming task.

Bug: 1033656
Change-Id: I4490690cafb290997b3b243d2423a78a113763f3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1965733Reviewed-by: Rohit Rao <rohitrao@chromium.org>
Commit-Queue: Maksym Onufriienko <monufriienko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#736581}

ios/build/bots/tests/eg2_tests.json

@@ -23,7 +23,7 @@
             "app": "ios_chrome_ui_eg2tests_module",
             "host": "ios_chrome_eg2tests",
             "shards": 2,
-            "shard size": 20
+            "swarming tasks": 2
         },
         {
             "app": "ios_chrome_web_eg2tests_module",

ios/build/bots/tests/eg_cq_tests.json

@@ -5,13 +5,13 @@
   "tests": [
     {
       "app": "ios_chrome_integration_egtests",
-      "shard size": 7,
+      "swarming tasks": 3,
       "xcode parallelization": true,
       "shards": 1
     },
     {
       "app": "ios_chrome_ui_egtests",
-      "shard size": 7,
+      "swarming tasks": 5,
       "xcode parallelization": true,
       "shards": 2
     },

ios/build/bots/tests/eg_tests.json

@@ -18,7 +18,7 @@
       "app": "ios_chrome_settings_egtests",
       "xcode parallelization": true,
       "shards": 1,
-      "shard size": 5
+      "swarming tasks": 3
     },
     {
       "app": "ios_chrome_translate_egtests",