Do not force mmacosx-version-min flag

[scribam]

This should be handled by CMake with CMAKE_OSX_DEPLOYMENT_TARGET

[scribam]

Also fix the following warnings

ld: warning: object file (/Users/runner/work/discord-rpc/discord-rpc/builds/osx-static/examples/send-presence/CMakeFiles/send-presence.dir/send-presence.c.o) was built for newer 'macOS' version (14.0) than being linked (11.0)
ld: warning: object file (../../src/libdiscord-rpc.a2) was built for newer 'macOS' version (14.0) than being linked (11.0)
ld: warning: object file (../../src/libdiscord-rpc.a3) was built for newer 'macOS' version (14.0) than being linked (11.0)
ld: warning: object file (../../src/libdiscord-rpc.a4) was built for newer 'macOS' version (14.0) than being linked (11.0)
ld: warning: object file (../../src/libdiscord-rpc.a5) was built for newer 'macOS' version (14.0) than being linked (11.0)
ld: warning: object file (../../src/libdiscord-rpc.a6) was built for newer 'macOS' version (14.0) than being linked (11.0)

in https://github.com/harmonytf/discord-rpc/actions/runs/10115234476/job/27975531733#step:7:59 and

ld: warning: object file (/Users/runner/work/discord-rpc/discord-rpc/builds/osx-dynamic/src/CMakeFiles/discord-rpc.dir/discord_rpc.cpp.o) was built for newer 'macOS' version (14.0) than being linked (11.0)
ld: warning: object file (/Users/runner/work/discord-rpc/discord-rpc/builds/osx-dynamic/src/CMakeFiles/discord-rpc.dir/rpc_connection.cpp.o) was built for newer 'macOS' version (14.0) than being linked (11.0)
ld: warning: object file (/Users/runner/work/discord-rpc/discord-rpc/builds/osx-dynamic/src/CMakeFiles/discord-rpc.dir/serialization.cpp.o) was built for newer 'macOS' version (14.0) than being linked (11.0)
ld: warning: object file (/Users/runner/work/discord-rpc/discord-rpc/builds/osx-dynamic/src/CMakeFiles/discord-rpc.dir/connection_unix.cpp.o) was built for newer 'macOS' version (14.0) than being linked (11.0)
ld: warning: object file (/Users/runner/work/discord-rpc/discord-rpc/builds/osx-dynamic/src/CMakeFiles/discord-rpc.dir/discord_register_osx.m.o) was built for newer 'macOS' version (14.0) than being linked (11.0)

in https://github.com/harmonytf/discord-rpc/actions/runs/10115234476/job/27975531733#step:7:95