[LIT] Migrate compiler lit config to the internal shell (#24883)

Part of #24607, following #24794 and #24810.

Same change as the last two: drops execute_external /
force_execute_external from compiler/lit.cfg.py. No RUN lines needed
touching.

Assisted-by: Claude Code

Signed-off-by: Zohaib Shah <zohaib.shah.2047@gmail.com>

compiler/lit.cfg.py

diff --git a/compiler/lit.cfg.py b/compiler/lit.cfg.py
index 81bc517..e0c9133 100644
--- a/compiler/lit.cfg.py
+++ b/compiler/lit.cfg.py
@@ -17,9 +17,7 @@
 
 config.name = "IREE"
 config.suffixes = [".mlir", ".txt"]
-config.test_format = lit.formats.ShTest(
-    execute_external=True, force_execute_external=True
-)
+config.test_format = lit.formats.ShTest()
 
 # Forward all IREE environment variables, as well as some passthroughs.
 # Note: env vars are case-insensitive on Windows, so check matches carefully.