build: Remove deprecated CMAKE_SKIP_BUILD_RPATH and SKIP_BUILD_RPATH settings

[151henry151]

Summary

This PR removes deprecated CMake RPATH settings that are no longer needed after improvements to the Guix build process. These settings were originally added as workarounds for binary checks performed before installation, but are now redundant.

Changes

• Remove CMAKE_SKIP_BUILD_RPATH TRUE from main CMakeLists.txt
• Remove SKIP_BUILD_RPATH OFF property setting from src/CMakeLists.txt (bitcoin-chainstate executable)
• Update TODO comments to reflect that these settings have been removed
• Preserve NetBSD-specific logic - CMAKE_INSTALL_RPATH_USE_LINK_PATH TRUE is still needed for that platform

Background

These settings were originally added as workarounds for a specific issue in the Guix build system:

1. Original Problem: Guix was performing binary checks (verifying executables) before the installation step
2. Issue: During these checks, executables had RPATHs pointing to temporary build directories (e.g., /tmp/build/...)
3. Workaround: Disable RPATH embedding during build so binaries wouldn't have these temporary paths

Why This Can Be Removed Now

Recent improvements to the build process have made these workarounds unnecessary:

• PR contrib: add R(UN)PATH check to ELF symbol-check bitcoin/bitcoin#30312: Added RPATH/RUNPATH checks to ELF symbol-check script
• PR cmake: Always provide RPATH on NetBSD bitcoin/bitcoin#31543: Made RPATH handling NetBSD-specific
• PR Add bitcoin-{node,gui} to release binaries for IPC bitcoin/bitcoin#31802: Added bitcoin-node/gui to release binaries, which involved reordering build steps
• Guix improvements: Binary checks now happen after installation, eliminating the temporary path issue

Testing

• ✅ Build verification: Successfully builds on Linux (Debian)
• ✅ NetBSD preservation: NetBSD-specific RPATH logic remains intact
• ✅ No functional changes: This is a cleanup that doesn't affect runtime behavior

Related Discussions

• cmake: Do not add rpath information to compiled executables hebasto/bitcoin#236 (comment)
• contrib: add R(UN)PATH check to ELF symbol-check bitcoin/bitcoin#30312 (comment)

Checklist

• This is a focused change (build system cleanup only)
• No functional changes to Bitcoin Core behavior
• Builds successfully on Linux
• Preserves necessary platform-specific logic (NetBSD)
• Updates relevant documentation/comments
• Follows Bitcoin Core coding style guidelines

Notes for Reviewers

This is a straightforward cleanup PR that removes deprecated CMake settings. The changes are minimal and well-documented. The NetBSD-specific logic is preserved as it's still needed for that platform.

This addresses the TODO items mentioned in:

• CMakeLists.txt:620
• src/CMakeLists.txt:412