chore(j7-perf): flatten useless include

Move _Release_Specific_Kernel_Performance_Guide ->
Release_Specific_Kernel_Performance_Guide and fix the toc. This file was
previously being named differently from every other platform.

Signed-off-by: Randolph Sapp <[email protected]>

Author: StaticRocket

source/devices/J7_Family/linux/Release_Specific.rst

@@ -6,7 +6,7 @@ Release Specific
    :maxdepth: 5
 
    Release_Specific_Release_Notes
-   Release_Specific_Performance_Guide
+   Release_Specific_Kernel_Performance_Guide
    Release_Specific_Yocto_layer_Configuration
    Release_Specific_Supported_Platforms_and_Versions
    Release_Specific_Migration_Guide