repotest: remove extension

The commit openbmc/openbmc@4e8877ee removed the extension as the default
variant of this script name.  Update the tools to match.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: If19b5f9e70aa2d7dd15be9aab70a6263b057aad0
diff --git a/build-setup.sh b/build-setup.sh
index c05da98..cae0b3b 100755
--- a/build-setup.sh
+++ b/build-setup.sh
@@ -138,7 +138,7 @@
 fi
 
 if [[ "$target" = repotest ]]; then
-  "${obmc_dir}"/meta-phosphor/scripts/run-repotest.sh
+  "${obmc_dir}"/meta-phosphor/scripts/run-repotest
   exit
 fi