Revert "Remove navigator.deviceMemory (part 1)"

[fmarier]

Fixes brave/brave-browser#12289

This reverts commit 740b4e3 which was added in #3669 to fix brave/brave-browser#1157.

Submitter Checklist:

• Submitted a ticket for my issue if one did not already exist.
• Used Github auto-closing keywords in the commit message.
• Added/updated tests for this change (for new code or code which already has tests).
• Verified that these changes build without errors on
  • Android
  • iOS
  • Linux
  • macOS
  • Windows
• Verified that these changes pass automated tests (unit, browser, security tests) on
  • iOS
  • Linux
  • macOS
  • Windows
• Verified that all lint errors/warnings are resolved (npm run lint, npm run gn_check)
• Ran git rebase master (if needed).
• Ran git rebase -i to squash commits (if needed).
• Tagged reviewers and labelled the pull request as needed.
• Requested a security/privacy review as needed.
• Added appropriate QA labels (QA/Yes or QA/No) to the associated issue
• Added appropriate release note labels (release-notes/include or release-notes/exclude) to the associated issue
• Public documentation has been updated as necessary. For instance:
  • https://github.com/brave/brave-browser/wiki/Deviations-from-Chromium-(features-we-disable-or-remove)
  • https://github.com/brave/brave-browser/wiki/Proxy-redirected-URLs
  • https://github.com/brave/brave-browser/wiki/Fingerprinting-Protections
  • https://github.com/brave/brave-browser/wiki/Brave%E2%80%99s-Use-of-Referral-Codes
  • https://github.com/brave/brave-browser/wiki/Custom-Headers
  • https://github.com/brave/brave-browser/wiki/Web-compatibility-issues-with-tracking-protection
  • https://github.com/brave/brave-browser/wiki/QA-Guide

Test Plan:

Testing is not 100% reliable, but the idea is to compare a current version of Brave with this build:

1. Using Nightly (without this PR), clear all cookies, history, etc.
2. Open the devtool console and type navigator.deviceMemory (should return undefined).
3. Log into Paypal and suffer through the CAPTCHA.
4. Using this build, clear all cookies, history, etc.
5. Open the devtool console and type navigator.deviceMemory (should return a number).
6. Log into Paypal and you shouldn't get a CAPTCHA.
7. Open https://antoinevastel.com/bots/ and confirm that everything is green at the bottom:
   
8. Open https://arh.antoinevastel.com/bots/areyouheadless and confirm that it says "You are not Chrome headless".

Reviewer Checklist:

• New files have MPL-2.0 license header.
• Request a security/privacy review as needed.
• Adequate test coverage exists to prevent regressions
• Verify test plan is specified in PR before merging to source

After-merge Checklist:

• The associated issue milestone is set to the smallest version that the
  changes has landed on.
• All relevant documentation has been updated.

[mkarolin]

#6962
#6964
Seem to be covering the same issue.

[mkarolin]

++

[kjozwiak]

Verification PASSED on macOS 10.15.7 x64 using the following build:

• verified that navigator.deviceMemory returns a number via the DevTools rather than undefined
• visited https://antoinevastel.com/bots/ and verified that everything appeared green

Note: this doesn't fix the reCAPTCHA issue so you'll still most likely see CAPTCHA's until that's resolved