Remove unnecessary `GEM_PATH` modification #615

Job	Run time
omnibus compilations, trigger	3s
omnibus compilations, #2	30m 38s
omnibus compilations, #1	28m 26s
omnibus compilations, #4	25m 30s
omnibus compilations, #10	27m 5s
omnibus compilations, #8	26m 35s
omnibus compilations, #3	26m 17s
omnibus compilations, #5	26m 52s
omnibus compilations, #6	27m 9s
omnibus compilations, #7	25m 39s
omnibus compilations, #12	24m 51s
omnibus compilations, #9	26m 42s
omnibus compilations, #11	26m 5s
omnibus compilations, result	4s
	5h 21m 56s

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