For #4969: Removes erroneous FxA sign up ping

[sblatz]

Pull Request checklist

• Quality: This PR builds and passes detekt/ktlint checks (A pre-push hook is recommended)
• Tests: This PR includes thorough tests or an explanation of why it does not
• Accessibility: The code in this PR follows accessibility best practices or does not include any user facing features

[codecov-io]

Codecov Report

Merging #4970 into master will increase coverage by <.01%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##             master   #4970      +/-   ##
===========================================
+ Coverage      8.08%   8.08%   +<.01%     
  Complexity      176     176              
===========================================
  Files           222     222              
  Lines          9017    9012       -5     
  Branches       1320    1318       -2     
===========================================
  Hits            729     729              
+ Misses         8236    8231       -5     
  Partials         52      52

Impacted Files	Coverage Δ	Complexity Δ
...la/fenix/components/metrics/GleanMetricsService.kt	0% <ø> (ø)	0 <0> (ø)	⬇️
...org/mozilla/fenix/components/BackgroundServices.kt	0% <ø> (ø)	0 <0> (ø)	⬇️
...va/org/mozilla/fenix/components/metrics/Metrics.kt	18.75% <ø> (+0.1%)	0 <0> (ø)	⬇️
...fenix/components/metrics/LeanplumMetricsService.kt	0% <ø> (ø)	0 <0> (ø)	⬇️

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[ekager]

CC @boek because you know much more than I do about where things need to be added/removed for telemetry