The functions find_em_expr_for_rel and ts_find_em_expr_for_rel are
identical. This patch removes find_em_expr_for_rel and changes all
call-sites to use ts_find_em_expr_for_rel.

Remove ts_dimension_info_create_open_interval_usec function because
it was no longer used. This patch also moves the add_dimension record
attribute numbers into the c file because it does not need to be
exported.

During refactoring continuous aggregates some function defintions
for functions that got removed were not removed from the header
file. Additionally a few other header files had function definitions
that no longer had an implementation or macros that were not used.