refactor(server): Simplify cleaning up the subscription diagnostics o… #1047

Job	Run time
Debug Build & Unit Tests (gcc)	3m 57s
Debug Build & Unit Tests (gcc, 32bit)	3m 48s
Debug Build & Unit Tests without Subscriptions (gcc)	2m 18s
Debug Build & Unit Tests with Diagnostics (gcc)	3m 2s
Debug Build & Unit Tests with multithreading (gcc)	2m 36s
Debug Build & Unit Tests with Alarms&Conditions (gcc)	13m 12s
Debug Build & Unit Tests (clang)	5m 44s
Debug Build & Unit Tests (tcc)	2m 41s
Encryption (MbedTLS) Build & Unit Tests (gcc)	3m 11s
PubSub Encryption (MbedTLS) Build & Unit Tests (gcc)	3m 19s
PubSub SKS Build & Unit Tests (gcc)	4m 54s
Encryption (OpenSSL) Build & Unit Tests (gcc)	2m 44s
Encryption (LibreSSL) Build & Unit Tests (gcc)	4m 56s
TPM Tool Build	3m 4s
Release Build	1m 28s
Amalgamation Build	1m 7s
Amalgamation Build with Multithreading	1m 8s
Valgrind Build & Unit Tests with MbedTLS (gcc)	16m 51s
Valgrind Build & Unit Tests with OpenSSL (gcc)	17m 38s
Valgrind Examples with MbedTLS (gcc)	1h 9m 16s
Valgrind Examples with OpenSSL (gcc)	1h 14m 53s
Clang Static Analyzer	4m 15s
Build All Companion Specifications	15m 2s
	4h 21m 4s

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