web installer: do not use blobs for storing extracted images

[octocorvus]

The total actual storage space used by the web installer is somewhere around 7-8GB (tested on Windows, assuming similar usage on other platforms). Most of the space is occupied by extracted images, which we store using blobs. On Android, blob storage quota is determined mainly by the total size of the disk. Currently, this limit is 6% of the total disk size (+ tiny 1% of total memory). So, an Android phone with 128GB of total storage will have only ~7.68GB of blob storage space available. This is problematic, as we might hit this limit sooner or later, causing installation to fail (even if more than enough storage space is available). Also, it isn't currently possible to use web installer using an Android phone with 64GB of total storage, as we're limited by blob storage quota (~3.84GB).

This also need to fixed in https://github.com/GrapheneOS/fastboot.js