This patch enables flake8 rule E502:
"the backslash is redundant between brackets" in toolkit/components/telemetry
by removing the relative E502 entry from toolkit/components/telemetry/.flake8
and fixing the files for which the E502 error was reported.
Precisely 8 errors violating E502 rule were found and solved.
MozReview-Commit-ID: 1z8f3JjJ2gt