combine trackers blocked and ads blocked on NTP

[cezaraugusto]

close brave/brave-browser#5273

Test Plan:

1. Before checking out this branch, open NTP and check the number of ads and trackers blocked
2. Check out this branch, open NTP and assert the current value is the sum of your previous stats of ads and trackers

The combination of ads and trackers is now called "trackers blocked" only, per brave/brave-browser#5273 (comment).

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.

[imptrx]

Tested and verified that ads and trackers blocked are now aggregated into one number - checkouts on storybooks too

nit: while we are on this issue, I was wondering if it be possible to keep #B02FFB (purple) as the color rather than #4C54D2 (blue) IMO the blue is hard to differentiate with certain background images and this holds especially true with the gradient 😅

So:

Rather than:

[cezaraugusto]

@imptrx good one. @karenkliu thoughts on #2950 (review)?

[karenkliu]

@imptrx Please set the label to be "Ads and Trackers blocked" for now and use #A0A5EB (light purple) instead of the blue. (This is a stopgap measure until we work on fixing the labels so that it matches the Shields panel labels).

[rebron]

Let's stick with "Ads and Trackers blocked" for now as @karenkliu mentioned and can revisit labels to match shields later. We'll surely get questions on the removal of "Ads blocked" and fewer questions if simply combining the labels.

[cezaraugusto]

updated

[imptrx]

Verified new text and combined tracker 🛳️🇮🇹