third_party/marl: Remove googletest submodule.

Having submodules inside subtrees breaks submodule update.

Bug: b/140546382
Change-Id: I0e3e9591bfd1aa8813d1e8764f702d87c5ac5e84
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/36030
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Tested-by: Ben Clayton <bclayton@google.com>

third_party/marl/third_party/googletest

diff --git a/third_party/marl/third_party/googletest b/third_party/marl/third_party/googletest
deleted file mode 160000
index fb49e6c..0000000
--- a/third_party/marl/third_party/googletest
+++ /dev/null
@@ -1 +0,0 @@
-Subproject commit fb49e6c164490a227bbb7cf5223b846c836a0305