On GitLab.com, InfluxSampler#sample_objects appears to take 1.2 s or so to
iterate through 1059 objects. This had led to delays of a couple hundred
milliseconds in processing in the main thread. Remove this code since it's not
really being used.

Closes gitlab-com/infrastructure#3250

+ change string concatenation to help with GC pressure.
+ fix metric producing incompatible label sets

Until https://gitlab.com/gitlab-org/prometheus-client-mmap/merge_requests/11
is ready, Prometheus metrics will not work and cause issues such as #40457.

Adds a rubocop rule (with autocorrect) to ensure line break after guard clauses.

This reverts commit d5859bb9.
This reverts commit 2b7e03cf.
This reverts commit 7799a9bc.

as are all other Transaction implementations

Use Mutex to guard metrics creation in transaction. Switch action view to threadsafe instance variables

+ remove deprecated test suite

+ fix cpu time