Add delete method for IndexLens on strings #674

Job	Run time
Documentation	1m 13s
Julia lts - macOS-latest - - pull_request	1m 27s
Julia lts - windows-latest - - pull_request	2m 42s
Julia 1 - ubuntu-latest - - pull_request	4m 12s
Julia 1 - macOS-latest - - pull_request	2m 41s
Julia pre - macOS-latest - - pull_request	2m 28s
Julia pre - windows-latest - - pull_request	4m 36s
Julia 1 - windows-latest - - pull_request	5m 16s
Julia lts - ubuntu-latest - - pull_request	2m 14s
Julia pre - ubuntu-latest - - pull_request	3m 43s
	30m 32s

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