JOBSET: unused copper layers are always exported in PDF
# Description
When using jobset to export PDF, unused copper layers are exported, leading to plotting of filled circles where there are holes in the board. This can eventually hide texts or graphics.
Notice this is also the case when exported to Gerbers but a weaker problem as they are filtered out and not plotted.
# Steps to reproduce
1. With any board with through-hole components, create a jobset and add a "PCB: Export PDF" job
2. In the job, only include "F.Fab" layer
3. Eventually set a destination and generate it
4. => In the output file, filled circles appear at every location of a through hole
5. => In the jobset file (in a text editor), you can see the below layer list for the job (example with a 4-layer board, so In1 and In2 are used and so do not appear)
```
"layers": [
"In30.Cu",
"In29.Cu",
"In28.Cu",
"In27.Cu",
"In26.Cu",
"In25.Cu",
"In24.Cu",
"In23.Cu",
"In22.Cu",
"In21.Cu",
"In20.Cu",
"In19.Cu",
"In18.Cu",
"In17.Cu",
"In16.Cu",
"In15.Cu",
"In14.Cu",
"In13.Cu",
"In12.Cu",
"In11.Cu",
"In10.Cu",
"In9.Cu",
"In8.Cu",
"In7.Cu",
"In6.Cu",
"In5.Cu",
"In4.Cu",
"In3.Cu",
"F.Fab"
],
```
# KiCad Version
```
Application: KiCad PCB Editor x64 on x64
Version: 9.0.1-rc2, release build
Libraries:
wxWidgets 3.2.6
FreeType 2.13.3
HarfBuzz 10.2.0
FontConfig 2.15.0
libcurl/8.11.1-DEV Schannel zlib/1.3.1
Platform: Windows 10 (build 19045), 64-bit edition, 64 bit, Little endian, wxMSW
OpenGL: Intel, Intel(R) UHD Graphics 630, 4.6.0 - Build 27.20.100.9664
Build Info:
Date: Mar 25 2025 11:36:18
wxWidgets: 3.2.6 (wchar_t,wx containers)
Boost: 1.86.0
OCC: 7.8.1
Curl: 8.11.1-DEV
ngspice: 44
Compiler: Visual C++ 1942 without C++ ABI
KICAD_IPC_API=ON
Locale:
Lang: en_GB
Enc: UTF-8
Num: 1,234.5
Encoded кΩ丈: D0BACEA9E4B888 (sys), D0BACEA9E4B888 (utf8)
```
issue