Update copyright notices to use Linux Foundation guidance

As a result, the copyright of contributors other than Arm is now
acknowledged, and the years of publishing are no longer tracked in the
source files.

Also remove the now-redundant lines declaring that the files are part of
MbedTLS.

This commit was generated using the following script:

# ========================
#!/bin/sh

# Find files
find '(' -path './.git' -o -path './3rdparty' ')' -prune -o -type f -print | xargs sed -bi '

# Replace copyright attribution line
s/Copyright.*Arm.*/Copyright The Mbed TLS Contributors/I

# Remove redundant declaration and the preceding line
$!N
/This file is part of Mbed TLS/Id
P
D
'
# ========================

Signed-off-by: Bence Szépkúti <bence.szepkuti@arm.com>
diff --git a/programs/psa/crypto_examples.c b/programs/psa/crypto_examples.c
index 97beb0e..623a090 100644
--- a/programs/psa/crypto_examples.c
+++ b/programs/psa/crypto_examples.c
@@ -1,5 +1,5 @@
 /*
- *  Copyright (C) 2018-2019, ARM Limited, All Rights Reserved
+ *  Copyright The Mbed TLS Contributors
  *  SPDX-License-Identifier: Apache-2.0
  *
  *  Licensed under the Apache License, Version 2.0 (the "License"); you may
@@ -13,8 +13,6 @@
  *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  *  See the License for the specific language governing permissions and
  *  limitations under the License.
- *
- *  This file is part of mbed TLS (https://tls.mbed.org)
  */
 
 #include "psa/crypto.h"
diff --git a/programs/psa/key_ladder_demo.c b/programs/psa/key_ladder_demo.c
index b633f75..ae2442e 100644
--- a/programs/psa/key_ladder_demo.c
+++ b/programs/psa/key_ladder_demo.c
@@ -31,7 +31,7 @@
  */
 
 /*
- *  Copyright (C) 2018, ARM Limited, All Rights Reserved
+ *  Copyright The Mbed TLS Contributors
  *  SPDX-License-Identifier: Apache-2.0
  *
  *  Licensed under the Apache License, Version 2.0 (the "License"); you may
@@ -45,8 +45,6 @@
  *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  *  See the License for the specific language governing permissions and
  *  limitations under the License.
- *
- *  This file is part of mbed TLS (https://tls.mbed.org)
  */
 
 /* First include Mbed TLS headers to get the Mbed TLS configuration and
diff --git a/programs/psa/key_ladder_demo.sh b/programs/psa/key_ladder_demo.sh
index fc2ef33..67de085 100755
--- a/programs/psa/key_ladder_demo.sh
+++ b/programs/psa/key_ladder_demo.sh
@@ -1,6 +1,6 @@
 #!/bin/sh
 #
-# Copyright (C) 2018, Arm Limited, All Rights Reserved
+# Copyright The Mbed TLS Contributors
 # SPDX-License-Identifier: Apache-2.0
 #
 # Licensed under the Apache License, Version 2.0 (the "License"); you may
@@ -14,8 +14,6 @@
 # WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
-#
-# This file is part of Mbed TLS (https://tls.mbed.org)
 
 set -e -u
 
diff --git a/programs/psa/psa_constant_names.c b/programs/psa/psa_constant_names.c
index 5fc4f9e..14d4494 100644
--- a/programs/psa/psa_constant_names.c
+++ b/programs/psa/psa_constant_names.c
@@ -1,5 +1,5 @@
 /*
- *  Copyright (C) 2018-2019, ARM Limited, All Rights Reserved
+ *  Copyright The Mbed TLS Contributors
  *  SPDX-License-Identifier: Apache-2.0
  *
  *  Licensed under the Apache License, Version 2.0 (the "License"); you may
@@ -13,8 +13,6 @@
  *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  *  See the License for the specific language governing permissions and
  *  limitations under the License.
- *
- *  This file is part of mbed TLS (https://tls.mbed.org)
  */
 
 #include <errno.h>