Explore removing memory tool section from system prompt for Gemini 3 #18556
Description
In packages/core/src/prompts/snippets.ts, there is a section about the memory tool in the system prompt (rendered by toolUsageRememberingFacts). This was previously needed for the Gemini 2.5 model series, but may no longer be necessary for Gemini 3. We should explore removing it to reduce prompt tokens and simplify the system instructions.