[snap] Fix versioning (#5727)

* fix snap versioning

* no need to install git as build packages

snap/snapcraft.yaml

@@ -1,7 +1,6 @@
 name: flatbuffers
 base: core18
-version: latest
-version-script: git describe --always | sed -e 's/-/+git/;y/-/./' | tail -c +2
+version: git
 summary: FlatBuffers compiler
 description: |
   FlatBuffers compiler
@@ -27,8 +26,6 @@ parts:
       - -DCMAKE_BUILD_TYPE=Release
     build-packages:
       - g++
-      # used to set version number
-      - git
 
 apps:
   flatc: