Double header in fpr_table_cv_summary_memo

[NewGraphEnvironment]

As per #68 we can fix with addition of label = NA in
knitr::kable(label = NA)

Besides fpr_make_html_tbl (now not on cran due to Envirometrix/plotKML#14) fpr_table_cv_summary_memo is only table that uses knitr::kable raw vs fpr_kable. That is why it is still double captioning after #68 was addressed.

Best solution seems to be to call fpr_kable here as well. Tests indicate that is fine.

#74 is seperate issue so will deal with in separate commit edit: this is not the relevant at all.