Don't run the GH workflows on shedule

We're no loger adding new functionalities to the `tbtc` 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.

Author: michalinacienciala

.github/workflows/contracts.yml

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

.github/workflows/relay.yml

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