Remove unnecessary --warn-shared-textrel flags.

This flag has never done anything for ld.lld, since it has this behavior
by default (and actually can't turn it off either). It's now being
removed as a valid flag from ld.lld, so it's time for Android to drop
the unnecessary flags. See https://reviews.llvm.org/D118942.

Test: builds
Change-Id: I22c344b7a55e275c1fbd5fef25f85e97a39de5c4

cc/config/x86_linux_bionic_host.go

@@ -47,7 +47,6 @@ var (
 		"-Wl,-z,relro",
 		"-Wl,-z,now",
 		"-Wl,--build-id=md5",
-		"-Wl,--warn-shared-textrel",
 		"-Wl,--fatal-warnings",
 		"-Wl,--hash-style=gnu",
 		"-Wl,--no-undefined-version",