Simplify Spring's @RequestMapping for GET requests.

Automated with the following one-liners:
git grep -l 'import.*RequestMethod' | while read F; do grep -q 'RequestMethod.POST' "$F" || sed -i '/import.*RequestMethod/d' "$F"; done
git grep -l 'RequestMethod\.GET' | xargs sed -i 's|(value = \([^,]\+\), method = RequestMethod.GET)|(\1)|'

No functional changes.