[ParserOutput] Remove unused TOCHTML from ParserCache serialization
This reverts commit
b4cf4aa6bd3a4b874ab665cebd8261ab88bbee8d,
which is no longer needed for ParserCache compatibility across
trains. REL1_42 contains
b4cf4aa6bd3a4b874ab665cebd8261ab88bbee8d,
so MW 1.43 will not need this.
This also adds new serialization test cases for 1.43 with this field
removed; see
https://www.mediawiki.org/wiki/Manual:Parser_cache/Serialization_compatibility
Change-Id: I716e2efe7a491002e6e6b2300016165fffe3c0d6