scripts: generate_rust_analyzer: remove sysroot assertion

scripts: generate_rust_analyzer: remove sysroot assertion

With nixpkgs's rustc, rust-src component is not bundled
with the compiler by default and is instead provided from
a separate store path, so this assumption does not hold.

The assertion assumes these paths are in the same location
which causes `make LLVM=1 rust-analyzer` to fail on NixOS.

Link: https://rust-for-linux.zulipchat.com/#narrow/stream/x/topic/x/near/565284250
Signed-off-by: Onur Özkan <work@onurozkan.dev>
Reviewed-by: Gary Guo <gary@garyguo.net>
Fixes: fe992163575b ("rust: Support latest version of `rust-analyzer`")
Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20251224135343.32476-1-work@onurozkan.dev
[ Reworded title. - Miguel ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>