about favicons are taking up way too much space in the session store

[bridiver]

Test plan

#10001 (comment)

1. Fresh profile
2. Open about:preferences, about:history and about:bookmarks
3. Close Brave
4. Open session-store-1 file in notepad, vim, etc
5. Confirm about page entries are NOT saving favicon using the data URL syntax for their favicon

Original issue description

• Did you search for similar issues before submitting this one?
  Yes

• Describe the issue you encountered:
  A fresh profile that opens about:preferences, about:history and about:bookmarks is ~180K

• Platform (Win7, 8, 10? macOS? Linux distro?):
  All

• Brave Version (revision SHA):

• Steps to reproduce:

  1. Fresh profile
  2. Open about:preferences, about:history and about:bookmarks
  3. Close Brave

• Actual result:
  session store is huge
  If you open the session-store-1 file, you WILL see about pages using the data URL syntax for their favicon.

• Expected result:
  session store should not be huge
  If you open the session-store-1 file, you WON'T see about pages using the data URL syntax for their favicon.

[NejcZdovc]

congrats on 10000 issue 🎉 🎉