Disable targets, where we use Nix packages.

--- a/utils/build-presets.ini
+++ b/utils/build-presets.ini
@@ -776,8 +776,6 @@
 llbuild
 swiftpm
 xctest
-libicu
-libcxx

 dash-dash

@@ -785,9 +785,7 @@
 install-llbuild
 install-swiftpm
 install-xctest
-install-libicu
 install-prefix=%(install_prefix)s
-install-libcxx
 install-sourcekit-lsp
 build-swift-static-stdlib
 build-swift-static-sdk-overlay