Revert "Mute git-commit messages to make pass insert readable"

This reverts commit f30ce637.

I decided I like the git output. Instead highlight generated passwords
using nice terminal output instead.

`pass generate' prints 10 lines of output, with only 2 related
to the operation at hand:
% pass generate xyz
1
2  You need a passphrase to unlock the secret key for
3  user: USER <EMAIL>
4  4096-bit RSA key, ID XYZ, created 1234-56-78
5
6  [master 12345] Added generated password for xyz to store.
7  1 file changed, 0 insertions(+), 0 deletions(-)
8   create mode 100644 xyz.gpg
9  The generated password to xyz is:
10 Some password 123
%

This patch takes care of 3 of 8 noise lines.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

In fact, if we're running from the source directory, just auto-detect
the platform file in the first place.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

The new environment variable, PASSWORD_STORE_PLATFORM_FILE is now used
for loading custom platform files while pass lives as
src/password-store.sh. After it is installed using 'make install', this
environment variable is no longer used, and either no platform file is
loaded (if the default platform is acceptable), or a hardcoded
also-installed platform file is referenced.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>