[mips64] Remove a useless declaration of Operand.

Change-Id: I5144d8315b5c1aca751d138e4d87240b703dc9e3
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3650359
Commit-Queue: Zhao Jiazhong <zhaojiazhong-hf@loongson.cn>
Auto-Submit: Yu Liu <liuyu@loongson.cn>
Reviewed-by: Zhao Jiazhong <zhaojiazhong-hf@loongson.cn>
Cr-Commit-Position: refs/heads/main@{#80585}

src/codegen/mips64/assembler-mips64.h

@@ -71,7 +71,6 @@ class Operand {
       : rm_(no_reg), rmode_(RelocInfo::EXTERNAL_REFERENCE) {
     value_.immediate = static_cast<int64_t>(f.address());
   }
-  V8_INLINE explicit Operand(const char* s);
   explicit Operand(Handle<HeapObject> handle);
   V8_INLINE explicit Operand(Smi value)
       : rm_(no_reg), rmode_(RelocInfo::NO_INFO) {