[lldb-vscode] Don't use SBLaunchInfo in request_attach

If LLDB attaches to an already running target, then structure SBAttachInfo is
used instead of SBLaunchInfo. lldb-vscode function request_attach sets some
values to g_vsc.launch_info, however this field is then not passed anywhere, so
this action has no effect. This commit removes invocation of
SBLaunchInfo::SetDetachOnError, which has no equivalent in SBAttachInfo.

File package.json doesn't describe detachOnError property for "attach" request
type, therefore it is not needed to update it.

Differential Revision: https://reviews.llvm.org/D76351