Remove SWIFT_FORCE_TEST_NEW_DRIVER=1 workaround

`Concurrency/Runtime/custom_main_executor.swift` is failing because
`-executor-factory` driver option is added only in the legacy driver but
the corresponding change in the new driver is not yet merged.
swiftlang/swift-driver#1861

The swiftlang/swift test suite by default uses the legacy driver, so
let's just align with them.

Author: kateinoigakukun

schemes/main/build/run-test.sh

@@ -6,5 +6,4 @@ SOURCE_PATH="$(cd "$(dirname "$0")/../../../.." && pwd)"
 TARGET_BUILD_ROOT="$SOURCE_PATH/build/WebAssembly"
 
 HOST_SUFFIX=$(find "$TARGET_BUILD_ROOT" -name "wasmstdlib-*" -exec basename {} \; | sed 's/wasmstdlib-//')
-# Force using the new driver for testing until https://github.com/swiftlang/swift-driver/pull/1756
-env SWIFT_FORCE_TEST_NEW_DRIVER=1 "PATH=$TARGET_BUILD_ROOT/llvm-$HOST_SUFFIX/bin:$PATH" "LIT_FILTER_OUT=(IRGen/|embedded/)" ninja check-swift-wasi-wasm32-custom -C "$TARGET_BUILD_ROOT/wasmstdlib-$HOST_SUFFIX"
+env "PATH=$TARGET_BUILD_ROOT/llvm-$HOST_SUFFIX/bin:$PATH" "LIT_FILTER_OUT=(IRGen/|embedded/)" ninja check-swift-wasi-wasm32-custom -C "$TARGET_BUILD_ROOT/wasmstdlib-$HOST_SUFFIX"