[build] Remove intermediate pipeline so that we can guarantee that we always have a fresh swift-dispatch when running swift tests.

In the fullness of time, we want to split the full build-script-impl pipeline so
that we can begin moving library like products (libdispatch, foundation) from
build-script-impl into build-script. We are not there yet since some of swift's
concurrency tests have a dependency on swift dispatch being built. This breaks
the build and we need to extract those tests into a separate product. But for
now, this makes sense to repair the build.

rdar://89046735

utils/swift_build_support/swift_build_support/build_script_invocation.py

@@ -603,7 +603,7 @@ class BuildScriptInvocation(object):
         # the build-script code base. The main difference is that these are all
         # build, tested, and installed all at once instead of performing build,
         # test, install like a normal build-script product.
-        builder.begin_impl_pipeline(should_run_epilogue_operations=False)
+        builder.begin_impl_pipeline(should_run_epilogue_operations=True)
 
         builder.add_impl_product(products.LibCXX,
                                  is_enabled=self.args.build_libcxx)
@@ -613,11 +613,6 @@ class BuildScriptInvocation(object):
                                  is_enabled=self.args.build_swift)
         builder.add_impl_product(products.LLDB,
                                  is_enabled=self.args.build_lldb)
-
-        # Begin a new build-script-impl pipeline that builds libraries that we
-        # build as part of build-script-impl but that we should eventually move
-        # onto build-script products.
-        builder.begin_impl_pipeline(should_run_epilogue_operations=True)
         builder.add_impl_product(products.LibDispatch,
                                  is_enabled=self.args.build_libdispatch)
         builder.add_impl_product(products.Foundation,