appveyor: fix PX4 version format check

by removing shallow clone such that we can infer the version from the
last tag

appveyor.yml

@@ -1,7 +1,6 @@
 # Build version
 version: "{build}"
-# shallow clone the main repo
+# do not shallow clone because we want to infer the version from the last tag
-clone_depth: 1
 
 branches:
   only:
@@ -36,7 +35,7 @@ build_script:
 # safe the repopath for switching to it in cygwin bash
 - for /f %%i in ('cygpath -u %%CD%%') do set repopath=%%i
 # build the make target
-- call bash --login -c "cd $repopath && git fetch --tags && make $PX4_CONFIG"
+- call bash --login -c "cd $repopath && make $PX4_CONFIG"
 
 # Note: using bash --login is important
 # because otherwise certain things (like python; import numpy) do not work