Remove --load-language

It has not been needed since 9.1, we support 9.1 and higher,
and it has been removed from Postgres 13. Resolves #248.

Makefile

@@ -341,7 +341,7 @@ test: test-serial test-parallel
 TB_DIR = test/build
 GENERATED_SCHEDULE_DEPS = $(TB_DIR)/all_tests $(TB_DIR)/exclude_tests
 REGRESS = --schedule $(TB_DIR)/run.sch # Set this again just to be safe
-REGRESS_OPTS = --inputdir=test --load-language=plpgsql --max-connections=$(PARALLEL_CONN) --schedule $(SETUP_SCH) $(REGRESS_CONF)
+REGRESS_OPTS = --inputdir=test --max-connections=$(PARALLEL_CONN) --schedule $(SETUP_SCH) $(REGRESS_CONF)
 SETUP_SCH = test/schedule/main.sch # schedule to use for test setup; this can be forcibly changed by some targets!
 IGNORE_TESTS = $(notdir $(EXCLUDE_TEST_FILES:.sql=))
 PARALLEL_TESTS = $(filter-out $(IGNORE_TESTS),$(filter-out $(SERIAL_TESTS),$(ALL_TESTS)))