[apps] Fixed verbose linkage difference.

[maxsharabayko]

• Verbose log now has a single version with a mutex lock.
• Removed SRT_ENABLE_VERBOSE_LOCK build definition.

Fixes #2145.

Notes

I am not quite sure if the implementation of the Verbose::Log with a mutex is thread safe given the template <class V> Log& operator<<(const V& arg) is not protected by a mutex lock. What's protected is putting the end of line symbol on log destruction.

Verb() << VerbLock << "Starting TargetMedium: " << this;

[ethouris]

Ok, let me explain.

The locking was normally not necessary, and the only merit for logging is to prevent printing from different threads to be interleaved. Verb is simply redirecting to the stream (cout or cerr, depending on settings) and it's by definition thread-safe. This locking is only necessary to keep one line not interrupted by printing of the other and prevent messup in the verbose messages.

Therefore it's only required in apps that uses threads and may have a situtation of printing Verb from multiple threads simultaneously. Apps like srt-test-live don't use multiple threads and so they don't use this locking.