PsbNew: misleading layer name in layer rescue warning dialogue

Description

When loading a board containing unknown layers, pcbnew offers to rescue them to "Cmts.User". However, this does not exists any more and is "User.Comments" now. "Cmts.User" is invisible to the user.

Steps to reproduce

1. Open a board containig an unknown layer, e.g. "Edge.c(!)uts", as I did due to a typo
2. See that rescuing to "Cmts.User" is offered

KiCad Version

Application: Pcbnew

Version: (5.99.0-3941-ga8bd0a9b84), release build

Libraries:
	wxWidgets 3.0.5
	libcurl/7.71.0 OpenSSL/1.1.1g (Schannel) zlib/1.2.11 brotli/1.0.7 libidn2/2.3.0 libpsl/0.21.0 (+libidn2/2.3.0) libssh2/1.9.0 nghttp2/1.41.0

Platform: Windows 8 (build 9200), 64-bit edition, 64 bit, Little endian, wxMSW

Build Info:
	Date: Oct 10 2020 21:08:24
	wxWidgets: 3.0.5 (wchar_t,wx containers,compatible with 2.8)
	Boost: 1.73.0
	OCE: 6.9.1
	Curl: 7.71.0
	ngspice: 32
	Compiler: GCC 10.2.0 with C++ ABI 1014

Build settings:
	KICAD_SCRIPTING=ON
	KICAD_SCRIPTING_MODULES=ON
	KICAD_SCRIPTING_PYTHON3=OFF
	KICAD_SCRIPTING_WXPYTHON=ON
	KICAD_SCRIPTING_WXPYTHON_PHOENIX=OFF
	KICAD_SCRIPTING_ACTION_MENU=ON
	BUILD_GITHUB_PLUGIN=ON
	KICAD_USE_OCE=ON
	KICAD_SPICE=ON