Removed some unnecessary backslashes in Bash code

Vagrantfile

@@ -13,8 +13,8 @@ Vagrant.configure("2") do |config|
 
     config.vm.provision "shell", inline: <<-SHELL
         fetch_and_check() { # Src: https://github.com/dmotte/misc
-            local c s; c=$(curl -fsSL "$1"; echo x) && \
-            s=$(echo -n "${c%x}" | sha256sum | cut -d' ' -f1) && \
+            local c s; c=$(curl -fsSL "$1"; echo x) &&
+            s=$(echo -n "${c%x}" | sha256sum | cut -d' ' -f1) &&
             if [ "$s" = "$2" ]; then echo -n "${c%x}"
             else echo "Checksum verification failed for $1: got $s, expected $2" >&2
             return 1; fi
@@ -26,21 +26,21 @@ Vagrant.configure("2") do |config|
 
         fetch_and_check \
             'https://www.virtualbox.org/download/oracle_vbox_2016.asc' \
-            '49e6801d45f6536232c11be6cdb43fa8e0198538d29d1075a7e10165e1fbafe2' | \
+            '49e6801d45f6536232c11be6cdb43fa8e0198538d29d1075a7e10165e1fbafe2' |
             gpg --dearmor -o /etc/apt/trusted.gpg.d/virtualbox.gpg
         echo 'deb [arch=amd64 signed-by=/etc/apt/trusted.gpg.d/virtualbox.gpg]' \
-            "https://download.virtualbox.org/virtualbox/debian $codename contrib" | \
+            "https://download.virtualbox.org/virtualbox/debian $codename contrib" |
             tee /etc/apt/sources.list.d/virtualbox.list
         apt-get update; apt-get install -y virtualbox-7.0
         # Note: a reboot is required before being able to use VirtualBox
 
         # Ref: https://developer.hashicorp.com/vagrant/install#Linux
         fetch_and_check \
             'https://apt.releases.hashicorp.com/gpg' \
-            'cafb01beac341bf2a9ba89793e6dd2468110291adfbb6c62ed11a0cde6c09029' | \
+            'cafb01beac341bf2a9ba89793e6dd2468110291adfbb6c62ed11a0cde6c09029' |
             gpg --dearmor -o /etc/apt/trusted.gpg.d/hashicorp.gpg
         echo 'deb [signed-by=/etc/apt/trusted.gpg.d/hashicorp.gpg]' \
-            "https://apt.releases.hashicorp.com $codename main" | \
+            "https://apt.releases.hashicorp.com $codename main" |
             tee /etc/apt/sources.list.d/hashicorp.list
         apt-get update; apt-get install -y vagrant
     SHELL