Replace use of if-let and when-let, obsolete in Emacs 31.0.50 #330

Job	Run time
Compile / Get matrix	46s
Compile / Compile using Emacs 29.4	38s
Compile / Compile using Emacs 29.3	38s
Compile / Compile using Emacs 29.2	40s
Compile / Compile using Emacs 29.1	37s
Compile / Compile using Emacs 28.2	34s
Compile / Compile using Emacs 28.1	37s
Compile / Compile using Emacs 27.2	29s
Compile / Compile using Emacs 27.1	30s
Compile / Compile using Emacs 26.3	28s
Compile / Compile using Emacs 26.2	36s
Compile / Compile using Emacs 26.1	28s
Compile / Compile using Emacs release-snapshot	35s
Compile / Compile using Emacs snapshot	27s
	8m 3s

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