Remove `MatrixClient.initLegacyCrypto` #10761

Job	Run time
Analyse Dead Code	18s
JSDoc Checker	31s
ESLint	43s
Node.js example	34s
Typescript Syntax Check	31s
Workflow Lint	19s
Downstream tsc element-web	0s
Downstream Typescript Syntax Check	1s
	2m 57s

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