Remove orphaned ExchangeMitigations.md

Script was removed in commit 1c33bb8 (Remove obsolete scripts) but the
doc was left behind. ExchangeMitigations.ps1 was superseded by EOMT.ps1.

Author: dpaulson45

docs/Security/ExchangeMitigations.md

@@ -123,12 +123,11 @@ nav:
       - Security/CVE-2023-23397/index.md
       - FAQ: Security/CVE-2023-23397/FAQ.md
     - ConfigureFipFsTextExtractionOverrides: Security/ConfigureFipFsTextExtractionOverrides.md
+    - EOMT: Security/EOMT.md
     - EOMT (Legacy): Security/EOMT-Legacy.md
     - EOMTv2 (Legacy): Security/EOMTv2-Legacy.md
-    - EOMT: Security/EOMT.md
     - Extended Protection: Security/Extended-Protection.md
     - ExchangeExtendedProtectionManagement: Security/ExchangeExtendedProtectionManagement.md
-    - ExchangeMitigations: Security/ExchangeMitigations.md
     - Test-CVE-2021-34470: Security/Test-CVE-2021-34470.md
     - Test-ProxyLogon: Security/Test-ProxyLogon.md
   - Setup: