。
It's so obvious it doesn't need proving.
Literal
Obvious-too-much-[and-so-て] proof [object-を] require-not.
~すぎて creates a cause-result chain: 'so excessively X that Y.' 要する is a formal Sino-Japanese verb meaning 'to require,' considerably more literary than 必要とする or いる. The negative 要しない gives this a terse, written feel — everyday speech would say 証明する必要はない.