remove add_revenue_split()

[cjyetman]

add_revenue_split() is no longer used anywhere:
https://github.com/search?q=org%3ARMI-PACTA+add_revenue_split+NOT+is%3Aarchived+&type=code

Its use in workflow.transition.monitor was removed in RMI-PACTA/workflow.transition.monitor#142

and some unexpected behavior of it was re-implemented manually in web_tool_script_1.R here:
https://github.com/RMI-PACTA/workflow.transition.monitor/blob/5fbe241de91accdb47295ef7032ae3e97c0c519f/web_tool_script_1.R#L97-L106

# FIXME: this is necessary because pacta.portfolio.allocate::add_revenue_split()
#  was removed in #142, but later we realized that it had a sort of hidden
#  behavior where if there is no revenue data it maps the security_mapped_sector
#  column of the portfolio data to financial_sector, which is necessary later
portfolio <-
  portfolio %>%
  mutate(
    has_revenue_data = FALSE,
    financial_sector = .data$security_mapped_sector
  )

in RMI-PACTA/workflow.transition.monitor#149