Revert "Boot: Add workaround to not fetch MCUboot's submodules"

This reverts commit 1655ef5120e99c62782575d0a8b3707ebfc2148e.

Reason for revert: Causes occasional build failures

Change-Id: I6269558656657f2613052f7a481057f1f4b57ce0
diff --git a/lib/ext/mcuboot/CMakeLists.txt b/lib/ext/mcuboot/CMakeLists.txt
index 92618be..822843f 100644
--- a/lib/ext/mcuboot/CMakeLists.txt
+++ b/lib/ext/mcuboot/CMakeLists.txt
@@ -19,9 +19,7 @@
         GIT_TAG ${MCUBOOT_VERSION}
         GIT_SHALLOW FALSE
         GIT_PROGRESS TRUE
-        GIT_SUBMODULES "docs" # Workaround for
-                              # https://gitlab.kitware.com/cmake/cmake/-/issues/20579
-                              # in cmake 3.17 and below.
+        GIT_SUBMODULES ""
     )
     # ToDo: set GIT_SHALLOW to 'TRUE' when MCUBOOT_VERSION will be set to a tag
     # (instead of a commit hash) with the new release.