Delete Erlang backend from configure.

configure.ac:
m4/mercury.m4:
    Delete --enable-erlang-grade configure option.

    Don't search for erlang compiler and interpreter.

    Don't substitute @ERLC@ and @ERL@.

    Don't add erlang to libgrades.

    Don't generate erlang_conf.hrl

library/erlang_conf.hrl.in:
    Delete template file.

.dockerignore:
browser/MDB_FLAGS.in:
compiler/COMP_FLAGS.in:
deep_profiler/DEEP_FLAGS.in:
library/.gitignore:
library/Mmakefile:
library/library.m:
mdbcomp/MDBCOMP_FLAGS.in:
mfilterjavac/MFILTERJAVAC_FLAGS.in:
profiler/PROF_FLAGS.in:
scripts/Mercury.config*.in:
scripts/mercury_config.in:
scripts/prepare_install_dir.in:
ssdb/SSDB_FLAGS.in:
tools/bootcheck:
    Delete references to Erlang .hrl files.

    Delete references to @ERLC@ and @ERL@.

.dockerignore

@@ -25,7 +25,6 @@ configure.log
 *.date0
 *.date3
 *.dll
-erlang_conf.hrl
 *.err
 *.exe
 /.git/*