Bad reference counting and DCHECK in IPFS Extension API

[iefremov]

Extension functions in ipfs_api.h use Unretained pointers and manual AddRef() Release() that are not actually needed, because functions are refcounted on their own, and can be bound to callbacks as is.

Moreover, there is a wrong balance of AddRef() and Release() somewhere that leads to DCHECK / memleak

STR:

1. open brave://settings/ipfs/keys
2. Start node
3. manually add key named "123"
4. open dev tools and type chrome.ipfs.addIpnsKey("123", () => console.log("aaa")) in console

[1735628:1735628:0520/205438.728179:FATAL:ref_counted.h(194)] Check failed: !in_dtor_. 
#0 0x7fc2f226b659 base::debug::CollectStackTrace()
#1 0x7fc2f216a3f3 base::debug::StackTrace::StackTrace()
#2 0x7fc2f218a963 logging::LogMessage::~LogMessage()
#3 0x7fc2f218b30e logging::LogMessage::~LogMessage()
#4 0x55e73ef07ba3 base::subtle::RefCountedThreadSafeBase::AddRef()
#5 0x55e73fc7f858 extensions::api::IpfsAddIpnsKeyFunction::Run()
#6 0x55e73f28a0c7 ExtensionFunction::RunWithValidation()
#7 0x55e73f28d9dc extensions::ExtensionFunctionDispatcher::DispatchWithCallbackInternal()
#8 0x55e73f28d354 extensions::ExtensionFunctionDispatcher::Dispatch()
#9 0x55e73f2b86d9 extensions::ExtensionWebContentsObserver::OnRequest()
#10 0x55e73f2b85e7 IPC::MessageT<>::Dispatch<>()
#11 0x55e73f2b84b7 extensions::ExtensionWebContentsObserver::OnMessageReceived()
#12 0x55e740dac70e extensions::ChromeExtensionWebContentsObserver::OnMessageReceived()

[iefremov]

@spylogsster pls take a look

[stephendonner]

Verified PASSED using the inline testplan with build

Brave	1.27.25 Chromium: 91.0.4472.77 (Official Build) nightly (x86_64)
Revision	1cecd5c8a856bc2a5adda436e7b84d8d21b339b6-refs/branch-heads/4472@{#1246}
OS	macOS Version 11.4 (Build 20F71)

Steps:

1. opened brave://settings/ipfs/keys
2. started my IPFS node via brave://ipfs-internals
3. manually added a new key named "123"
4. opened dev tools and typed chrome.ipfs.addIpnsKey("123", () => console.log("aaa")) in console

Confirmed I didn't crash; reproduced the crash very easily with an earlier nightly build, before this fix.

I now get undefined returned, with aaa printed to the console.

example	example