Remove redundant classes for import

[spylogsster]

After refactoring from brave/brave-core#8771 we do not need anymore dedicated classes.

Removed File/Text/Directory import classes, use base class instead
Move blob creation to network utilities
Avoid of base::Uretained

Test Case

• all types of IPFS import should work as expected: images, text, links, files, directories, videos

[stephendonner]

Marking as QA/Blocked until #15935 is verified fixed.

[stephendonner]

Marking as QA/Blocked until #15935 is verified fixed.

I conflated issues; this is working just fine, sorry!

Verified PASSED using

Brave	1.26.30 Chromium: 91.0.4472.57 (Official Build) nightly (x86_64)
Revision	e3443317fa07f1e9997e4a9c738eddfefc3c0292-refs/branch-heads/4472_54@{#6}
OS	macOS Version 11.3.1 (Build 20E241)

Steps:

Image

• loaded * ipfs://bafybeigdyrzt5sfp7udm7hu76uh7y26nf3efuylqabf3oclgtqy55fbzdi/
• right-clicked and chose Import to IPFS -> Selected image

Text

• loaded https://www.lipsum.com/ and scrolled down to the first lorem ipsum paragraph
• selected it and chose Import to IPFS -> Selected text

Link

• loaded https://archive.org/web/
• right-clicked on the Wayback Machine logo and choose Import to IPFS -> Linked content

Video

• loaded https://upload.wikimedia.org/wikipedia/commons/7/79/Big_Buck_Bunny_small.ogv
• right-clicked on the video and choose Import to IPFS -> Selected video

File

• loaded https://www.leaseweb.com/platform/network
• scrolled down to a 10MB file from a mirror, right-clicked on it and chose Import to IPFS -> Linked content

example	example	example	example	example	example	example

Image: https://bafybeigdyrzt5sfp7udm7hu76uh7y26nf3efuylqabf3oclgtqy55fbzdi.ipfs.dweb.link/?filename=bafybeigdyrzt5sfp7udm7hu76uh7y26nf3efuylqabf3oclgtqy55fbzdi.ipfs.localhost
Text: https://bafybeibjhmwnw2s47sr6xij2xj7thr7u7d3c2v7ckxecvvewolwha6zr3q.ipfs.dweb.link/?filename=www.lipsum.com_13828526949295533255
Link: https://bafybeiavuq4ixeuay3rprg4mb2ydlzmdb3qb3lbjt6b2od5hsiomy65gnq.ipfs.dweb.link/?filename=archive.org **Webpage:** https://bafybeieorrkovrjqdxv24xrvigpotqjljlytwxzubsl6tmh5ejf4fmlqa4.ipfs.dweb.link/?filename=www.wikipedia.org
Video: https://dweb.link/ipfs/QmaNvPDRmgT3xs7E5B9MQoZLxrqMtjfDnWnFrHHhyPzC9i?filename=Big_Buck_Bunny_small.ogv
File: https://dweb.link/ipfs/QmZAjR7E1qB4nD5T55F95thMLn2fG5C8tpUB2FMnVhS8Nn?filename=10mb.bin