ts_lua plugin document has incorrect 'context' information for the hook point constants

The section "Hook point constants" in ts_lua Plugin document provides the incorrect information on hook point constants being available to use ts.hook() function.

Like TS_LUA_HOOK_PRE_REMAP or TS_LUA_HOOK_READ_REQUEST_HDR constants are not useful to register the hook point in do_remap(). However, they can be used in do_global_txn_start() or do_global_read_request() to register for the hook call back functions. So, the 'context' information is irrelevant for this section.