Remove the "generic" register completion test. (llvm#82445)

For reasons that are not clear to me, on arm64, the alias registers are
listed in list of register info's we do completion against, but for
x86_64 they are not. Maybe this is a difference in how the dynamic
register builders work for the two systems. Anyway, it doesn't look
possible to make a generic one.

lldb/test/API/functionalities/completion/TestCompletion.py

@@ -787,27 +787,6 @@ def test_register_read_and_write_on_x86(self):
         # register write can only take exact one register name as argument
         self.complete_from_to("register write rbx ", [])
 
-    def test_register_read_and_write_generic(self):
-        """Test the completion of the commands register read and write on x86"""
-
-        self.build()
-        self.main_source_spec = lldb.SBFileSpec("main.cpp")
-        lldbutil.run_to_source_breakpoint(self, "// Break here", self.main_source_spec)
-
-        # test cases for register read
-        self.complete_from_to("register read f", ["fp"])
-        # register read can take multiple register names as arguments
-        self.complete_from_to("register read sp ", ["sp", "fp"])
-        # complete with prefix '$'
-        self.complete_from_to("register read sp $", ["$sp", "$fp"])
-        self.complete_from_to("register read $x0 ", ["sp", "fp"])
-
-        # test cases for register write
-        self.complete_from_to("register write ", ["fp", "sp"])
-        self.complete_from_to("register write f", ["fp"])
-        # register write can only take exact one register name as argument
-        self.complete_from_to("register write fp ", [])
-
     def test_common_completion_target_stophook_ids(self):
         subcommands = ["delete", "enable", "disable"]