[APM] Latency correlations: Do not include comparison date range

[sophiec20]

Kibana version:
Found in 7.14.0 BC1

Describe the bug:
When clicking "View Correlations" from the Overview tab for a service, the analysis date range appears to be from the start of the comparison window to the end of the main date picker.

The comparison option is not available in the Transaction or Errors tab, and clicking on "View Correlations" from here will only include the main date picker range.

Only the main date picker time range should be used for correlation analysis for the following reasons:

1. Including the comparison window will sometimes "double" the data being analysed which increases analysis run time. This becomes problematic when very long date ranges are being analysed or in environments already under perf strain.
2. The user probably did not intend to include the comparison period, as this provide insights when eyeballing time series charts (rather than latency distributions).
3. Making a change to the underlying correlation analysis code in order to compare time periods would be significant and if required, should be scheduled as a longer exercise.
4. It will match behaviour from the other tabs

Steps to reproduce:

Compare results when viewing correlations from each service tab, with and without comparison checked.

[elasticmachine]

Pinging @elastic/apm-ui (Team:apm)

[elasticmachine]

Pinging @elastic/ml-ui (:ml)