tests/CMakeLists.txt: Drop hardcoded -no-pie linker flags

[OPNA2608]

These cause the build to fail when… the compiler expects PIE usage: NixOS/nixpkgs#372768

[ 99%] Linking CXX executable test-gactionmuxer
/nix/store/j7p46r8v9gcpbxx89pbqlh61zhd33gzv-binutils-2.43.1/bin/ld: /nix/store/l89iqc7am6i60y8vk507zwrzxf0wcd3v-gcc-14-20241116/lib/gcc/x86_64-unknown-linux-gnu/14.2.1/crtbegin.o: relocation R_X86_64_32 against hidden symbol `__TMC_END__' can not be used when making a PIE object
/nix/store/j7p46r8v9gcpbxx89pbqlh61zhd33gzv-binutils-2.43.1/bin/ld: failed to set dynamic section sizes: bad value
collect2: error: ld returned 1 exit status
make[2]: *** [tests/CMakeFiles/test-gactionmuxer.dir/build.make:102: tests/test-gactionmuxer] Error 1

Is there a reason for these being there? They were introduced 4y ago, together with all of the CMake code. Building with & without PIE & running the resulting binaries seems to work fine once these are removed, at least in Nixpkgs.

[FliegendeWurst]

Can confirm that the PIE-enabled build passes the test suite.