Revert "Add the ability to source RBE related scripts from envsetup.sh"

This reverts commit 9aa9e47b8c3921037f779453341ae1a822d454ce.

Reason for revert: DroidMonitor-triggered revert due to breakage https://android-build.googleplex.com/builds/quarterdeck?branch=git_rvc-qpr-dev-plus-aosp&target=ndk&lkgb=7546337&lkbb=7546521&fkbb=7546426, bug https://buganizer.corp.google.com/issues/193566521

Fix: 193566521
Change-Id: I7196a00006499f729baa86a252b0df6535c6aeaa
diff --git a/rbesetup.sh b/rbesetup.sh
index 3b0e7cf..ec39e6e 100644
--- a/rbesetup.sh
+++ b/rbesetup.sh
@@ -24,11 +24,8 @@
 }
 
 # This function needs to run first as the remaining defining functions may be
-# using the envsetup.sh defined functions. Skip this part if this script is already
-# being invoked from envsetup.sh.
-if [[ "$1" != "--skip-envsetup" ]]; then
-  _source_env_setup_script || return
-fi
+# using the envsetup.sh defined functions.
+_source_env_setup_script || return
 
 # This function prefixes the given command with appropriate variables needed
 # for the build to be executed with RBE.