Delete Filesystem::GetTemporaryFolder.

Testcode updated to use webrtc::test::TempFilename.
Also deletes now unused functions AppleDataDirectory,
AppleTempDirectory and AppleAppName.

BUG=webrtc:6424

Review-Url: https://codereview.webrtc.org/2995413002
Cr-Original-Commit-Position: refs/heads/master@{#19483}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: a0c88878b6bfabc4a841d0756701af2ca1b1ad76
10 files changed