Clean up references to deprecated create_srcjar in android_resources

`create_srcjar = false` was needed during the transition to moving
R.java generation to android_library targets. Now this variable is
unused (the variable is asserted to be false), clean up all references.

Bug: chromium:1073476
Change-Id: I4c09ea05ded27ea2360392aacbce036bc1a2f928
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/185160
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Commit-Queue: Mohamed Heikal <mheikal@chromium.org>
Cr-Commit-Position: refs/heads/master@{#32178}

examples/BUILD.gn

@@ -188,7 +188,6 @@ if (is_android) {
       "androidapp/res/values/strings.xml",
       "androidapp/res/xml/preferences.xml",
     ]
-    create_srcjar = false
 
     # Needed for Bazel converter.
     custom_package = "org.appspot.apprtc"

examples/androidnativeapi/BUILD.gn

@@ -68,7 +68,6 @@ if (is_android) {
   android_resources("resources") {
     testonly = true
     custom_package = "org.webrtc.examples.androidnativeapi"
-    create_srcjar = false
     sources = [
       "res/layout/activity_main.xml",
       "res/values/strings.xml",

examples/androidvoip/BUILD.gn

@@ -76,7 +76,6 @@ if (is_android) {
   android_resources("resources") {
     testonly = true
     custom_package = "org.webrtc.examples.androidvoip"
-    create_srcjar = false
     sources = [
       "res/layout/activity_main.xml",
       "res/values/colors.xml",

rtc_tools/network_tester/BUILD.gn

@@ -133,7 +133,6 @@ if (is_android) {
   android_resources("NetworkTesterMobile_resources") {
     testonly = true
     custom_package = "com.google.media.networktester"
-    create_srcjar = false
     sources = [
       "androidapp/res/layout/activity_main.xml",
       "androidapp/res/mipmap-hdpi/ic_launcher.png",