Update Flutter.gitignore

remove IntelliJ related lines

Co-authored-by: Tim Hunter <thorrsson@github.com>

Flutter.gitignore

@@ -10,11 +10,6 @@
 .history
 .svn/
 
-# IntelliJ related
-*.iml
-*.ipr
-*.iws
-.idea/
 
 # Visual Studio Code related
 .classpath