[lldb] Fix modernize-use-equals-default warnings (NFC)

Fix modernize-use-equals-default warnings. Because this check is listed
in LLDB's top level .clang-tidy configuration, the check is enabled by
default and the resulting warnings show up in my editor.

I've audited the modified lines. This is not a blind change.

GitOrigin-RevId: 91688716ba49942051dccdf7b9c4f81a7ec8feaf
29 files changed