Don't backup or restore 'bluetooth_on' setting on watches

Setting 'bluetooth_on' to false during restore would cause watch OOBE to fail due to bluetooth connection loss.

Change-Id: I28a4a204eb3bbafdb0898066141f3d3ff846df7e
Tested: atest SettingsProviderTest:SettingsBackupAgentTest
Flag: EXEMPT bugfix
Bug: 355520239