Remove the check whether proj4 is an object #3
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This PR removes a check which seems to be incompatible with Rollup. I wrote more details here: GeoTIFF/georaster-layer-for-leaflet#109
I believe the removal of this check does not have negative consequences. If one of the remaining conditions,
typeof proj4.defs !== "function", is satisfied, then unless the body of theifis executed, the line below (proj4.defs(defs);) will fail. So doing the additional check (which I propose to remove) does not affect whether the code will throw an error.