Remove `MatrixClient.initLegacyCrypto` #10745

Job	Run time
ESLint	39s
JSDoc Checker	32s
Analyse Dead Code	18s
Node.js example	33s
Typescript Syntax Check	25s
Workflow Lint	18s
Downstream tsc element-web	0s
Downstream Typescript Syntax Check	1s
	2m 46s

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