Allow .d.ts with --isolatedModules

Fixes #29490

Author: sheetalkamat

src/compiler/program.ts

@@ -2809,10 +2809,6 @@ namespace ts {
             }
 
             if (options.isolatedModules) {
-                if (getEmitDeclarations(options)) {
-                    createDiagnosticForOptionName(Diagnostics.Option_0_cannot_be_specified_with_option_1, getEmitDeclarationOptionName(options), "isolatedModules");
-                }
-
                 if (options.out) {
                     createDiagnosticForOptionName(Diagnostics.Option_0_cannot_be_specified_with_option_1, "out", "isolatedModules");
                 }