Don't run the GH workflows on schedule

We're no longer adding new functionalities to the `keep-ecdsa` code, as this
repository is related to the `v1` of the system and is no longer used in `v2`.
There is no need to run the code-checking workflows every night.

.github/workflows/client.yml

@@ -1,8 +1,6 @@
 name: Go
 
 on:
-  schedule:
-    - cron: "0 0 * * *"
   push:
     branches:
       - main

.github/workflows/contracts.yml

@@ -1,8 +1,6 @@
 name: Solidity
 
 on:
-  schedule:
-    - cron: "0 0 * * *"
   push:
     branches:
       - main

.github/workflows/staker-rewards.yml

@@ -1,8 +1,6 @@
 name: Staker Rewards
 
 on:
-  schedule:
-    - cron: "0 0 * * *"
   push:
     branches:
       - main