xbps-src: don't export CCACHE_COMPRESS=1

[r-ricci]

ccache enables compression by default since version 4.0.
This variable is redundant and prevents disabling compression through
a config file (useful e.g. on compressed filesystems).

AFAIK there's no way to disable compression when CCACHE_COMPRESS is present, since the environment has the highest precedence, according to the manual:

The priorities of configuration options are as follows (where 1 is highest):

 1. Environment variables.

 2. The primary (cache-specific) configuration file (see below).

 3. The secondary (system-wide read-only) configuration file
     <sysconfdir>/ccache.conf (typically /etc/ccache.conf or
     /usr/local/etc/ccache.conf).

 5. Compile-time defaults.

Testing the changes

• I tested the changes in this PR: YES

[sgn]

Not sure but something like:

    if [ -z "${XBPS_CCACHE_NOCOMPRESS+set}" ]; then
        export CCACHE_COMPRESS=1
    fi

with XBPS_CCACHE_NOCOMPRESS from config file.

Disable ccache compression is NOT nice.

[r-ricci]

Disable ccache compression is NOT nice.

This PR doesn't disable compression. As I said, ccache enables compression by default [since version 4.0](https://ccache.dev/releasenotes.html#_ccache_4_0). Even if you want ccache to perform compression, this variable is redundant. Removing it changes nothing unless you add `compression = false` to `hostdir/ccache/ccache.conf`.