pgsql: Retire execdebug.h and its debugging facility

Retire execdebug.h and its debugging facility

execdebug.h includes "pretty old and crufty" code used to print
debugging information in the executor. As reported recently, this code
has not compiled in the last 10 years or so, and there are better
alternatives available, such as elog().

There is no indication that this facility is still being used, so remove
it along with its associated debugging macros:
EXEC_NESTLOOPDEBUG
EXEC_SORTDEBUG
EXEC_MERGEJOINDEBUG

Reviewed-by: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Reviewed-by: Tatsuya Kawata <kawatatatsuya0913(at)gmail(dot)com>
Discussion: https://postgr.es/m/aoFfAvp6xdk7Cdi6@paquier.xyz

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/617636328f5285fa2e0b7e42f4ae3cb0d82f8b5e

Modified Files
--------------
src/backend/executor/nodeIncrementalSort.c | 41 +--------
src/backend/executor/nodeMergejoin.c | 121 +--------------------------
src/backend/executor/nodeNestloop.c | 38 +--------
src/backend/executor/nodeSort.c | 27 +-----
src/backend/jit/llvm/llvmjit_expr.c | 1 -
src/include/executor/execdebug.h | 130 -----------------------------
6 files changed, 4 insertions(+), 354 deletions(-)