Update Github Actions workflows

This change removes some unneeded compilation flags for the kernel
builds.

In addition, we revert back to compilation level O2 based on the
discussion in the LKML:
https://lore.kernel.org/lkml/20200507224530.2993316-1-Jason@zx2c4.com/

.github/workflows/master.yml

@@ -14,7 +14,6 @@ jobs:
         include:
           - build_type: 'generic'
             build_cc: gcc-10
-            build_cflags: '-O3 -Wno-error=maybe-uninitialized'
     if: "!contains(github.event.head_commit.message, 'skip ci')"
     steps:
     - name: Checkout Sources

.github/workflows/release.yml

@@ -12,13 +12,13 @@ jobs:
         include:
           - build_type: 'generic'
             build_cc: gcc-10
-            build_cflags: '-O3 -Wno-error=maybe-uninitialized'
+            build_cflags: ''
           - build_type: zen2
             build_cc: gcc-10
-            build_cflags: '-O3 -march=znver2 -Wno-error=maybe-uninitialized'
+            build_cflags: '-march=znver2'
           - build_type: cascadelake
             build_cc: gcc-10
-            build_cflags: '-O3 -march=cascadelake -Wno-error=maybe-uninitialized'
+            build_cflags: '-march=cascadelake'
     steps:
     - name: Checkout Sources
       uses: actions/checkout@v2