This reverts commit bdc5548c
that introduced a work-around to ha_innobase::delete_table()
for avoiding failures when trying to remove table partitions.

This work-around (of not removing statistics in case of a locking
conflict) would occasionally cause a failure of the test
parts.part_supported_sql_func_innodb:

mysqltest: In included file "./suite/parts/inc/partition_supported_sql_funcs.inc":
included from ./suite/parts/inc/part_supported_sql_funcs_main.inc at line 91:
included from /buildbot/amd64-ubuntu-2004-msan/build/mysql-test/suite/parts/t/part_supported_sql_func_innodb.test at line 44:
At line 234: query 'alter table t66
reorganize partition s1 into
(partition p0 values less than ($valsqlfunc),
partition p1 values less than maxvalue)' failed: ER_DUP_KEY (1022): Can't write; duplicate key in table 'mysql.innodb_table_stats'