Remove confusing EXE_NAME environment variable

This removes the `EXE_NAME` variable in the release workflow,
replacing all uses of it with an literal `ein`, which was always
its value.

The rationale is that this variable was confusing in two ways:

- The release workflow builds and publishes two executables, for
  both the ein and gix commands. The executable for the ein
  command was specified through this environment variable, while
  the executable for the gix command was already given literally.
  Besides improving consistency, removing the environment variable
  makes clear what is actually being specified.

- The name of the executable that provides the ein command is `ein`
  on most operating systems but `ein.exe` on Windows. But the
  `EXE_NAME` variable always held the value `ein` on all systems,
  with a `.exe` suffix concatenated to it on Windows. This was
  unintuitive because `EXE_NAME` didn't always name an executable.

Author: EliahKagan

.github/workflows/release.yml

@@ -83,8 +83,6 @@ jobs:
       TARGET_DIR: ./target
       # Emit backtraces on panics.
       RUST_BACKTRACE: 1
-      # The name of the executable to expect
-      EXE_NAME: ein
     strategy:
       matrix:
         build: [ linux, linux-arm, macos, win-msvc, win-gnu, win32-msvc ]
@@ -184,7 +182,7 @@ jobs:
 
       - name: Strip release binary (linux and macos)
         if: matrix.build == 'linux' || matrix.build == 'macos'
-        run: strip target/${{ matrix.target }}/release/${{ env.EXE_NAME }} target/${{ matrix.target }}/release/gix
+        run: strip target/${{ matrix.target }}/release/ein target/${{ matrix.target }}/release/gix
 
       - name: Strip release binary (arm)
         if: matrix.build == 'linux-arm'
@@ -193,7 +191,7 @@ jobs:
             "$PWD/target:/target:Z" \
             rustembedded/cross:arm-unknown-linux-gnueabihf \
             arm-linux-gnueabihf-strip \
-            /target/arm-unknown-linux-gnueabihf/release/${{ env.EXE_NAME }} \
+            /target/arm-unknown-linux-gnueabihf/release/ein \
             /target/arm-unknown-linux-gnueabihf/release/gix
       - name: Build archive
         run: |
@@ -203,11 +201,11 @@ jobs:
           cp {README.md,LICENSE-*,CHANGELOG.md} "$staging/"
 
           if [ "${{ matrix.os }}" = "windows-latest" ]; then
-            cp target/release/${{ env.EXE_NAME }}.exe target/release/gix.exe "$staging/"
+            cp target/release/ein.exe target/release/gix.exe "$staging/"
             7z a "$staging.zip" "$staging"
             echo "ASSET=$staging.zip" >> $GITHUB_ENV
           else
-            cp target/${{ matrix.target }}/release/${{ env.EXE_NAME }} target/${{ matrix.target }}/release/gix "$staging/"
+            cp target/${{ matrix.target }}/release/ein target/${{ matrix.target }}/release/gix "$staging/"
             tar czf "$staging.tar.gz" "$staging"
             echo "ASSET=$staging.tar.gz" >> $GITHUB_ENV
           fi