cleanup: remove test include file, clarify the comment

mysql-test/include/fail_start_mysqld.inc

-# ==== Usage ====
-#
-# [--let $restart_parameters= --innodb-force-recovery=0 --innodb-read-only=1]
-# [--let $mysqld_stub_cmd= $MYSQLD_LAST_CMD]
-# [--let $error_log= $MYSQLTEST_VARDIR/log/mysqld.1.err]
-# --source include/fail_restart_mysqld.inc
-
-# Evaluate the default of $error_log
-if (!$error_log)
-{
-  --let $error_log= $MYSQLTEST_VARDIR/log/mysqld.1.err
-}
-
---error 1
---exec $mysqld_stub_cmd $restart_parameters >> $error_log  2>&1
-
-# As the server is stopped
---disable_reconnect

mysql-test/mysql-test-run.pl

@@ -5055,9 +5055,9 @@ sub mysqld_start ($$) {
   }
 
 
-  # "Dynamic" version of MYSQLD_CMD is reevaluated with each mysqld_start.
-  # Use it to restart the server at testing a failing server start (e.g
-  # due to incompatible options).
+  # Command line for mysqld started for *this particular test*.
+  # Differs from "generic" MYSQLD_CMD by including all command line
+  # options from *.opt and *.combination files.
   $ENV{'MYSQLD_LAST_CMD'}= "$exe  @$args";
 
   if ( $opt_gdb || $opt_manual_gdb )

mysql-test/r/tc_heuristic_recover.result

 call mtr.add_suppression("Can't init tc log");
 call mtr.add_suppression("Found 1 prepared transactions!");
 call mtr.add_suppression("Aborting");
-set debug_sync='RESET';
 CREATE TABLE t1 (i INT) ENGINE=InnoDB;
 SET GLOBAL innodb_flush_log_at_trx_commit=1;
 FLUSH TABLES;

mysql-test/t/tc_heuristic_recover.test

@@ -9,7 +9,7 @@
 # All this proves no crashes and effective rollback of the transaction.
 #
 --source include/have_innodb.inc
-# The test logics really requires --log-bin.
+# The test logic really requires --log-bin.
 --source include/have_binlog_format_mixed.inc
 --source include/have_debug_sync.inc
 --source include/not_embedded.inc
@@ -22,14 +22,7 @@ call mtr.add_suppression("Aborting");
 #
 # The "restart" expect-file facility can't be engaged because the server
 #  having conflicting options may not succeed to boot up.
-# Also notice $MYSQLD_CMD is too "static" being unaware of the actual options
-# of the last (before shutdown or kill) server run.
-# That's why $MYSQLD_LAST_CMD that allows for the server new start
-# with more options appended to a stub set which is settled at this very point.
---let $mysqld_stub_cmd= $MYSQLD_LAST_CMD
---let $error_log= $MYSQLTEST_VARDIR/log/mysqld.1.err
---let SEARCH_FILE= $error_log
-set debug_sync='RESET';
+--let SEARCH_FILE=$MYSQLTEST_VARDIR/log/mysqld.1.err
 
 CREATE TABLE t1 (i INT) ENGINE=InnoDB;
 SET GLOBAL innodb_flush_log_at_trx_commit=1;
@@ -55,8 +48,8 @@ SELECT * FROM t1;
 
 # TODO: MDEV-12700 Allow innodb_read_only startup without prior slow shutdown.
 --source include/kill_mysqld.inc
---let $restart_parameters= --innodb-force-recovery=4
---source include/fail_start_mysqld.inc
+--error 1
+--exec $MYSQLD_LAST_CMD --log-bin=master-bin --binlog-format=mixed --core-file --loose-debug-sync-timeout=300 --innodb-force-recovery=4
 
 --let SEARCH_PATTERN= was in the XA prepared state
 --source include/search_pattern_in_file.inc
@@ -65,8 +58,8 @@ SELECT * FROM t1;
 --let SEARCH_PATTERN= \\[ERROR\\] Can\\'t init tc log
 --source include/search_pattern_in_file.inc
 
---let $restart_parameters= --innodb-force-recovery=4 --tc-heuristic-recover=COMMIT
---source include/fail_start_mysqld.inc
+--error 1
+--exec $MYSQLD_LAST_CMD --log-bin=master-bin --binlog-format=mixed --core-file --loose-debug-sync-timeout=300 --innodb-force-recovery=4 --tc-heuristic-recover=COMMIT
 --let SEARCH_PATTERN= was in the XA prepared state
 --source include/search_pattern_in_file.inc
 --let SEARCH_PATTERN= Found 1 prepared transactions!
@@ -76,8 +69,8 @@ SELECT * FROM t1;
 --let SEARCH_PATTERN= Please restart mysqld without --tc-heuristic-recover
 --source include/search_pattern_in_file.inc
 
---let $restart_parameters= --tc-heuristic-recover=ROLLBACK
---source include/fail_start_mysqld.inc
+--error 1
+--exec $MYSQLD_LAST_CMD --log-bin=master-bin --binlog-format=mixed --core-file --loose-debug-sync-timeout=300 --tc-heuristic-recover=ROLLBACK
 
 --let SEARCH_PATTERN= was in the XA prepared state
 --source include/search_pattern_in_file.inc
@@ -88,7 +81,6 @@ SELECT * FROM t1;
 --let SEARCH_PATTERN= Please restart mysqld without --tc-heuristic-recover
 --source include/search_pattern_in_file.inc
 
---let $restart_parameters=
 --source include/start_mysqld.inc
 
 --let SEARCH_PATTERN= was in the XA prepared state