[Paradise] Fix local card decision metric for existing bin range.

If the user goes through checkout flow several times without closing the tab,
the local card migration manager won't be re-created which leads to the case
that the variable supported_card_bin_ranges pre-exist before GDFSC calls.

We do not filter the unsupported cards during GetMigratableCreditCards(). We
only call FilterOutUnsupportedLocalCards() when OnDidGetUploadDetails() for
checkout flow. We remove the local var of the supported bin ranges. If later
any usage of FilterOutUnsupportedLocalCards() outside OnDidGetUploadDetails,
we need to add back the local var.
Add some comments about these two functions to make it clearer.

Bug: 954367
Change-Id: I7fc7cbdecf76d25b34737ef6ddc25737f7540657
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1614456
Reviewed-by: Siyu An <siyua@chromium.org>
Reviewed-by: Jared Saul <jsaul@google.com>
Commit-Queue: Sujie Zhu <sujiezhu@google.com>
Cr-Commit-Position: refs/heads/master@{#661058}
2 files changed