Merge #18899: travis: Remove valgrind

fa082d0a57 travis: Remove valgrind (MarcoFalke)

Pull request description:

  When the valgrind run was added, it took 2 hours. Travis kindly raised the timeout limit to the maximum possible of 3 hours.

  Today, a full build of Bitcoin Core with all tests takes more than three hours. Thus, it is impossible to run all tests on travis.

  Moreover, the feedback loop for developers that create a pull request takes at least 2 hours, but in some cases (when the travis queue is full) until the next day. This is unacceptable.

  Fix both issues by removing the build from travis.

  Please note that the `ci/test/` configurations are *not* removed. They will stay in the repo and can be executed anywhere (just not on travis).

ACKs for top commit:
  jamesob:
    ACK fa082d0a57
  jnewbery:
    utACK fa082d0a57

Tree-SHA512: 9acaa0e2d3926014fadb7dd2e86c4e01df382e9399f6ae99f989fa609da66a77bdd1b75d6ff42d2686f38f730b8564e6dc722aa597a473290c9d30c2abe7ef0f

.travis.yml

@@ -143,21 +143,11 @@ jobs:
       env: >-
         FILE_ENV="./ci/test/00_setup_env_native_asan.sh"
 
-    - stage: test
-      name: 'x86_64 Linux  [GOAL: install]  [bionic]  [no depends, only system libs, valgrind]'
-      env: >-
-        FILE_ENV="./ci/test/00_setup_env_native_valgrind.sh"
-
     - stage: test
       name: 'x86_64 Linux  [GOAL: install]  [focal]  [no depends, only system libs, sanitizers: fuzzer,address,undefined]'
       env: >-
         FILE_ENV="./ci/test/00_setup_env_native_fuzz.sh"
 
-    - stage: test
-      name: 'x86_64 Linux  [GOAL: install]  [focal]  [no depends, only system libs, fuzzers under valgrind]'
-      env: >-
-        FILE_ENV="./ci/test/00_setup_env_native_fuzz_with_valgrind.sh"
-
     - stage: test
       name: 'x86_64 Linux  [GOAL: install]  [bionic]  [no wallet]'
       env: >-