Remove deprecated experimental-new-pass-manager flag.

https://reviews.llvm.org/D136789 removed this flag, it's been a no-op
since 15.0.0. The current Android compiler is 15.0.3, but upcoming
compilers will error on the fact that this flag doesn't exist any more.

Change-Id: I54666175b521ed5cdd76c53ed700ad4ddf6931da
Test: make
Bug: N/A

cc/config/global.go

@@ -76,9 +76,6 @@ var (
 		// Help catch common 32/64-bit errors.
 		"-Werror=int-conversion",
 
-		// Enable the new pass manager.
-		"-fexperimental-new-pass-manager",
-
 		// Disable overly aggressive warning for macros defined with a leading underscore
 		// This happens in AndroidConfig.h, which is included nearly everywhere.
 		// TODO: can we remove this now?