PaymentRequest: Remove the sequence version of supportedMethods (browser)

This is one of several patches that will remove the sequence version of
supportedMethods member. This patch stops using it by removing the
related code in browser side.
  - [1/2] https://crrev.com/c/1078687
  - [2/2] This patch

Intent to remove:
  https://groups.google.com/a/chromium.org/forum/#!topic/blink-dev/JAnUvBqXElU

Bug: 754779
Cq-Include-Trybots: luci.chromium.try:ios-simulator-full-configs;master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: Ia276a90240dc817e60ce8cf793454eb822e67a4e
Reviewed-on: https://chromium-review.googlesource.com/1108057
Reviewed-by: Mathieu Perreault <mathp@chromium.org>
Reviewed-by: Moe Ahmadi <mahmadi@chromium.org>
Reviewed-by: Ganggui Tang <gogerald@chromium.org>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Commit-Queue: Jinho Bang <jinho.bang@samsung.com>
Cr-Commit-Position: refs/heads/master@{#575862}
45 files changed