mergestate: remove unused unsupported related mergestate records

I tried to find users of this but was unable to find. Seems like RECORD_OVERRIDE
is doing for what they were used before.

Differential Revision: https://phab.mercurial-scm.org/D8718

mercurial/mergestate.py

@@ -53,8 +53,6 b" RECORD_PATH_CONFLICT = b'P'"
 
 RECORD_MERGE_DRIVER_STATE = b'm'
 RECORD_OVERRIDE = b't'
-RECORD_UNSUPPORTED_MANDATORY = b'X'
-RECORD_UNSUPPORTED_ADVISORY = b'x'
 
 MERGE_DRIVER_STATE_UNMARKED = b'u'
 MERGE_DRIVER_STATE_MARKED = b'm'
@@ -115,8 +113,6 b' class mergestate(object):'
     m: the external merge driver defined for this merge plus its run state
        (experimental)
     f: a (filename, dictionary) tuple of optional values for a given file
-    X: unsupported mandatory record type (used in tests)
-    x: unsupported advisory record type (used in tests)
     l: the labels for the parts of the merge.
 
     Merge driver run states (experimental):