pgsql: Remove PgStat_BackendFunctionEntry

Remove PgStat_BackendFunctionEntry

This structure included only PgStat_FunctionCounts, and removing it
facilitates some upcoming refactoring for pgstatfuncs.c to use more
macros rather that mostly-duplicated functions.

Author: Bertrand Drouvot
Reviewed-by: Nathan Bossart
Discussion: https://postgr.es/m/11d531fe-52fc-c6ea-7e8e-62f1b6ec626e@gmail.com

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/e731aeac8928592435f73465a03fae83a2db0ee2

Modified Files
--------------
src/backend/utils/activity/pgstat.c          |  2 +-
src/backend/utils/activity/pgstat_function.c | 20 ++++++++++----------
src/backend/utils/adt/pgstatfuncs.c          | 12 ++++++------
src/include/pgstat.h                         | 11 +----------
src/tools/pgindent/typedefs.list             |  1 -
5 files changed, 18 insertions(+), 28 deletions(-)