Revert addition of DYLIB-LLVM-AOT as a default backend (#2702)

This is a partial reversion of https://github.com/google/iree/pull/2639.
The change to Bazel build scripts was preserved to keep the uniform
environment between Bazel builds running with RBE.

Part of https://github.com/google/iree/issues/2645
diff --git a/CMakeLists.txt b/CMakeLists.txt
index c4c5504..b761338 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -116,7 +116,7 @@
 
 # List of all target backends to be built by default:
 set(IREE_ALL_TARGET_BACKENDS
-  DYLIB-LLVM-AOT
+  # TODO(#2645): Add DYLIB-LLVM-AOT when it doesn't require an env var
   LLVM-IR
   Vulkan-SPIRV
   VMLA
diff --git a/build_tools/bazel_to_cmake/bazel_to_cmake_converter.py b/build_tools/bazel_to_cmake/bazel_to_cmake_converter.py
index 9add36f..bc40c97 100644
--- a/build_tools/bazel_to_cmake/bazel_to_cmake_converter.py
+++ b/build_tools/bazel_to_cmake/bazel_to_cmake_converter.py
@@ -43,7 +43,6 @@
     self.FLATBUFFER_SUPPORTS_REFLECTIONS = False
     self.PLATFORM_VULKAN_LOADER_COPTS = []
     self.IREE_DRIVER_MODULES = [
-        "//iree/hal/dylib:dylib_driver_module",
         "//iree/hal/vmla:vmla_driver_module",
         "//iree/hal/vulkan:vulkan_driver_module",
         "//iree/hal/llvmjit:llvmjit_driver_module",
diff --git a/build_tools/cmake/iree_check_test.cmake b/build_tools/cmake/iree_check_test.cmake
index 82ac9c7..93fd934 100644
--- a/build_tools/cmake/iree_check_test.cmake
+++ b/build_tools/cmake/iree_check_test.cmake
@@ -243,8 +243,8 @@
   )
 
   if(NOT DEFINED _RULE_TARGET_BACKENDS AND NOT DEFINED _RULE_DRIVERS)
-    set(_RULE_TARGET_BACKENDS "vmla" "vulkan-spirv" "llvm-ir" "dylib-llvm-aot")
-    set(_RULE_DRIVERS "vmla" "vulkan" "llvm" "dylib")
+    set(_RULE_TARGET_BACKENDS "vmla" "vulkan-spirv" "llvm-ir")
+    set(_RULE_DRIVERS "vmla" "vulkan" "llvm")
   endif()
 
   list(LENGTH _RULE_TARGET_BACKENDS _TARGET_BACKEND_COUNT)
diff --git a/iree/modules/check/CMakeLists.txt b/iree/modules/check/CMakeLists.txt
index 0c6c103..0a016be 100644
--- a/iree/modules/check/CMakeLists.txt
+++ b/iree/modules/check/CMakeLists.txt
@@ -57,7 +57,6 @@
     iree::base::status
     iree::base::target_platform
     iree::base::tracing
-    iree::hal::dylib::dylib_driver_module
     iree::hal::llvmjit::llvmjit_driver_module
     iree::hal::vmla::vmla_driver_module
     iree::hal::vulkan::vulkan_driver_module